EMG Flashcards
While performing an EMG, you are listening to the right deltoid muscle at rest. You hear a regular sound that sounds like raindrops falling onto a tin roof. What is the most likely clinical implication for this muscle?
A Active denervation
B This is normal at rest
C Previous denervation followed by reinnervation
D Radiation plexopathy
A
The “rain drops on a tin roof” sound, when occurring at regular intervals while the muscle is at rest, is classic for fibrillations. Fibrillations indicate active denervation.
A 40 year-old female develops 4 days of progressive lower limb weakness. She has a history of recent upper respiratory tract infection. Bilateral lower limb EMG/NCS reveals normal sural nerve SNAPs (sensory nerve action potentials), but prolonged latency of bilateral superficial fibular nerve SNAPs. The bilateral CMAPs to the EDB and AH (compound muscle action potentials to the extensor digitorum brevis and abductor hallucis) show prolonged latency but normal amplitude. EMG reveals decreased recruitment in the bilateral EDB, AH, tibialis anterior, gastrocnemius, and semimembranosus, but normal activity in rectus femoris and adductor longus. Which of the following additional EMG/NCS findings would most likely be discovered in this patient?
AAll of these findings are equally likely to occur
BPersistent A-waves
CAbsent F-waves
DDecreased temporal dispersion
Answer: C
• This patient presents with Guillain-Barre Syndrome (GBS), also referred to as AIDP (acute inflammatory demyelinating polyradiculopathy). GBS is caused by a recent infection (typically GI or URI) causing your immune system to confuse a foreign protein with a protein on your own myelin. Thus, your body destroys your own peripheral nerve myelin (demyelinating the nerves and prolonging the latency).
• The first EDX finding of GBS is delayed or absent F-waves.
• NCS reveals prolonged latency and sometimes reduced amplitude of SNAPs with sural nerve sparing, as the sural nerve is larger with more myelin than other peripheral sensory nerves, and thus is less affected than the other nerves.
• CMAPs show prolonged latency, decreased conduction velocity (CV), and typically normal amplitude (this is a demyelinating disease primarily, not axonal loss).
• EMG shows decreased recruitment but otherwise there should be NO active denervation usually, but this can occur as a secondary feature of GBS weeks after onset.
• Treatment involves PT and early plasmapheresis/IVIG.
• Abnormal/increased temporal dispersion is also a feature of this disease on NCS, due to the widespread and more uniform demyelination of nerves taking place
• The presence of A-waves indicates that some reinnervation has taken place in the past, and would NOT be a criterion in diagnosing GBS.
During an EMG study, you notice on the screen that with forceful muscle contraction by the patient, there are 2 motor units displayed: one firing at 40 Hz, and the other firing at 50 Hz. Which of the following is the most likely diagnosis?
APolymyositis
BPost-polio syndrome
CDuchenne muscular dystrophy
DMyotonia congenita
Answer: B
Explanation:
• This question describes a decreased recruitment pattern, which can be found in cases of conduction block or axonal loss: essentially neuropathies.
• This is sometimes called a neuropathic recruitment pattern for this reason, as decreased recruitment is generally NOT seen in myopathies (the remaining answer choices).
• Post-polio syndrome is the death of anterior horn cells due to “burning out” over time, leaving the patient with few remaining active motor units, which leads to decreased recruitment and, thus, increased firing rate of existing motor units.
A 34 year-old female long distance runner presents to you with gradual onset bilateral anterior knee pain that she has had for several years. Her pain is worse when descending stairs. She has occasional knee stiffness after prolonged sitting. Knee x-rays demonstrate a shallow lateral patellofemoral contour; you initiate physical therapy involving vastus lateralis stretching and vastus medialis strengthening. After 5 months of physical therapy, kinesiotaping, relative rest, and NSAIDs, the pain is still not improving. What is the next best step?
A Referral to major academic center
B Surgery
C MRI
D Repeat x-rays
Answer: C
Explanation:
• This patient presents with classic patellofemoral pain syndrome (PFPS). This is abnormal patellar tracking due to muscle weakness and imbalances; specifically this involves vastus lateralis and IT band tightness in combination with vastus medialis weakness.
• Treatment involves vastus medialis strengthening with vastus lateralis and IT band stretching, along with hip girdle strengthening for stability.
• Sometimes patellar knee sleeves are used to assist with the proprioception of proper patellar tracking, as is kinesiotaping.
• The patellar grind test is described here, which is a test for PFPS.
• If rest, physical therapy, NSAIDs, and bracing do NOT improve the pain, MRI and surgery may be considered. The purpose of the MRI is to look for cartilage damage, e.g. chondromalacia patella, which is a sequela of PFPS in which the patellofemoral cartilage softens and degenerates due to improper patellar tracking.
• Note: typically this is the muscular pattern of weakness and tightness for PFPS, but it is possible to have a weak vastus lateralis and tight vastus medialis and perform essentially the opposite PT as for typical PFPS.
A 79 year-old female with history of diabetes mellitus (well controlled) presents to your clinic with complaints of right groin pain. She denies trauma. It has developed gradually over the past several months along with low back pain. She denies numbness or tingling, but feels weak in her right leg. On exam, strength is neurologically intact. There is no tenderness to palpation of the anterior, lateral, or posterior right hip. FABERE reproduces her right groin pain, but not back pain. What is the most appropriate next step?
A Corticosteroid injection
B Orthopedics consult
C Hip x-rays
D Physical therap
Answer: D
Explanation:
• This patient presents with classic gradual onset osteoarthritis of the hip.
• True hip pain manifests as groin pain. An aging individual with a history of presumably knee OA leading to total knee replacements and gradual onset groin pain without trauma is most likely indicating “wear and tear” femoroacetabular joint arthritis.
• The first step in suspected OA management is physical therapy. If physical therapy fails to improve function and/or pain, x-rays would be appropriate to determine the extent of femoroacetabular disease.
• A corticosteroid injection into the hip joint could also be considered at that point.
• Orthopedics should be consulted if this becomes a surgical case; i.e. if physical therapy and/or corticosteroid injection fail the patient and the patient has significant osteoarthritic joint disease on x-rays.
Which of the following is the most likely cause of a patient’s lumbosacral plexopathy?
A Pregnancy
B Rapid weight gain
C Diabetes mellitus
D Hypertension
Answer: C
Explanation:
• Of the following choices, diabetes is the most likely to cause lumbosacral plexopathy.
• Rapid weight gain and hypertension are typically not causes of plexopathy.
• Rapid weight gain or even loss can contribute to lateral femoral cutaneous neuropathy, however.
• Pregnancy in the third trimester can cause plexopathy due to pressure from the fetus, but this would not be nearly as common as diabetes.
• In particular, diabetes causes a condition called diabetic lumbosacral radiculoplexopathy.
• Poor blood sugar control in relation to a rapid weight loss (not gain!) causes this condition.
• Remember, plexopathies show variable NCS/EMG findings depending on which nerves are affected.
• Treatment involves blood sugar control and rehabilitation.
During nerve conduction studies, raising the low frequency filter will cause which of the following effects?
A No effect
B Decreased amplitude
C Increased peak latency
D Increased amplitude
Answer: B
Explanation:
• Raising the low frequency filter will decrease the amplitude, as will lowering the high frequency filter.
A patient’s right lower limb EMG/NCS results are as follows. Routine fibular and tibial motor/sensory nerve conduction studies are normal. EMG reveals decreased recruitment and polyphasic potentials in tibialis anterior, extensor hallucis longus, short head of biceps femoris, tensor fascia lata, fibularis longus, and tibialis posterior, but normal activity in vastus medialis, adductor longus, gastrocnemius, and abductor hallucis. Which of the following is the most likely diagnosis?
A L4 radiculopathy without reinnervation
B L4 radiculopathy with reinnervation
C L5 radiculopathy without reinnervation
D L5 radiculopathy with reinnervation
Answer: D
Explanation:
• L5 radiculopathy with reinnervation is the best answer.
• All L5-innervated muscles are affected (with polyphasic potentials, indicating early reinnervation taking place), but all muscles that do NOT share any L5 innervation are spared.
• Please refer to the innervation chart at the beginning of the Upper and Lower Extremity Peripheral Nervous System Diseases chapters for a detailed innervation guide.
During an EMG, you ask the patient to very lightly begin contracting their extensor indicis proprius. Instantly you notice the EMG screen become flooded with many small, short-duration MUAPs. Which of the following is the most likely diagnosis?
A Severe radial neuropathy at the elbow
B PLS
C ALS
D Polymyositis
Answer: D
Explanation:
• MUAPs = Motor Unit Action Potentials
• This question describes a myopathic recruitment pattern, or increased recruitment pattern.
• This is typically seen in myopathies, not neuropathies; thus, polymyositis is correct.
Which of the following is the key NCS/EMG finding, found in radiculopathies, that helps to differentiate a radiculopathy from more peripheral nerve lesions?
A Abnormal compound muscle action potentials
B Normal compound muscle action potentials
C Normal paraspinal resting activity
D Normal sensory nerve action potentials
Answer: D
Explanation:
• Normal SNAPs (sensory nerve action potentials) are the key NCS finding demonstrated in a radiculopathy.
• Because the dorsal root ganglion contains the cell bodies of the sensory neurons of a dermatome of a given limb, and these cells are bipolar neurons residing outside the spinal cord, any nerve injury proximal to these cell bodies (e.g. radiculopathy) will NOT affect the distally directed axons of these bipolar cells (i.e. the projections extending down the arm or leg from the dorsal root ganglion).
• Thus, these unaffected axons will conduct impulses quite normally, and SNAPs will be entirely normal in a pure radiculopathy.
• Paraspinal muscles corresponding to the affected nerve root level will theoretically show EMG changes (increased irritability, possible active denervation).
• CMAPs will be expected to potentially be abnormal, but this would NOT be the key differentiating feature of a radiculopathy.
A 67-year-old male with a history of cervical spondylosis presents with right hand paresthesias. His internist orders an EMG/NCS of his right upper extremity, which reveals absent median nerve SNAP (sensory nerve action potential) and positive sharp waves in the APB (abductor pollicis brevis) muscle during the needle exam. He undergoes surgical treatment. Following surgery, which of the following orthoses is most appropriate?
A Aspen collar
B Thumb spica splint
C Gel shell splint
D Soft cervical collar
Answer: C
Explanation:
• The patient has right hand paresthesias in the setting of severe median neuropathy findings on EMG (absent median nerve SNAP and active denervation of Abductor Pollicis Brevis (Positive Sharp Waves)) which indicates median neuropathy as the likely diagnosis.
• The most appropriate surgical intervention would be carpal tunnel release given the severity of the disease based on electrodiagnostic findings.
• Following carpal tunnel release, a gel shell splint is used; this is a nonarticular brace (doesn’t cross joint meaning it doesn’t restrict ROM) used to help prevent hypertrophy of the surgical scar by maintaining pressure against the healing incision.
• A thumb spica splint limits thumb ROM, and can be used for:
○ DeQuervain tenosynovitis
○ Skier’s thumb: an acute partial or complete rupture of the ulnar collateral ligament (UCL) of the thumb’s MCP joint due to a hyperabduction trauma of the thumb
○ Distal 2/3 scaphoid fractures
○ 1st CMC arthritis
The nerve that provides cutaneous sensation to the medial leg below the knee arises via which of the following ways?
A As a branch of the tibial nerve
B As the continuation of the femoral nerve
C As the continuation of the obturator nerve
D As a branch of the sciatic nerve
Answer: B
Explanation:
• The saphenous nerve is described here, and is the continuation of the femoral nerve after it has innervated all its muscles.
You are reviewing EMG/NCS results of a patient. The results demonstrate decreased proximal and distal amplitude with normal latency. EMG reveals decreased recruitment. Which of the following is the most likely etiology of these findings?
A Axonal loss
B Conduction block
C Demyelination
D Normal variant
Answer: A
Explanation:
• Decreased amplitude throughout an entire nerve’s length suggests axonal loss.
• EMG will show decreased recruitment in these cases.
• Conduction block is seen with proximally reduced amplitude, but stimulating distally beyond the spot of conduction block can demonstrate a normal “repaired” amplitude.
A primary difference between patients with spinal muscular atrophy (SMA) type 2 and patients with SMA type 3 is which of the following?
A Nusinersen is approved for type 2 disease, but not type 3 disease
B Patients with SMA type 3 can walk independently
C Type 2 disease shows long-duration, large amplitude motor unit action potentials (MUAPs)
D A different gene is affected between the two types
Answer: B
Explanation:
• Spinal Muscular Atrophy (all types) is caused by mutations in the SMN1 gene; all types can show a neuropathic EMG pattern (long duration, large amplitude MUAPs).
• Nusinersen is FDA-approved for all types of SMA.
• Patients with SMA 2 can sit but NOT stand independently.
• Patients with SMA 3 can stand and walk independently, at least for some time.
During an upper limb EMG, you notice prolonged SNAP latency to digit 5, dorsal ulnar cutaneous nerve, and medial antebrachial cutaneous nerve (MAC). Which of the following diagnoses do these findings indicate? AUlnar neuropathy at the wrist BMedial cord plexopathy CC8 radiculopathy DUlnar neuropathy at the elbow
Answer: B
Explanation:
• Of the answer choices, only medial cord plexopathy could explain an abnormal MAC.
• Radiculopathy produces normal SNAPs.
The ulnar nerve is formed distally to the medial cord, thus the DUC (dorsal ulnar cutaneous nerve) and digit 5 SNAP could be abnormal in medial cord plexopathy OR ulnar neuropathy at the elbow, but ulnar neuropathy at the elbow would produce a normal MAC (medial antebrachial cutaneous nerve) SNAP.
During a nerve conduction study you realize that the patient’s limb being studied is cold. Which of the following effects will this have on the waveform?
AIncreased amplitude, prolonged latency, increased duration
BIncreased amplitude, prolonged latency, decreased duration
CDecreased amplitude, shortened latency, decreased duration
DDecreased amplitude, prolonged latency, increased duration
Answer: A
Explanation:
• A cold limb will result in increased amplitude, prolonged latency (slow conduction velocity), and increased duration.
• When the limb is cold, channels stay open longer, causing a larger, heftier amplitude, and longer time of depolarizing.
During repetitive nerve stimulation (RNS), which of the following percentage decreases in the compound muscle action potential (CMAP) amplitude indicates that a neuromuscular junction (NMJ) disease is present? A>40 B>30 C>20 D>10
Answer: D
Explanation:
• A greater than 10% decrement in the CMAP amplitude during RNS (repetitive nerve stimulation) is a positive finding for NMJ disease (myasthenia gravis, Lambert-Eaton Syndrome, botulism).
Which of the following muscles receives its innervation from all roots (C5-T1) of the brachial plexus? AFlexor digitorum profundus BPectoralis major CLatissimus dorsi DTriceps brachii
Answer: B
Explanation:
• The pectoralis major is innervated by C5-T1 roots of the brachial plexus.
• Triceps and Latissimus dorsi are innervated by C6, C7, C8 roots.
• FDP (Flexor digitorum profundus) is innervated by C7, C8, T1 roots.
A 62 year-old male with a past medical history of hypertension presents with progressive onset weakness and swallowing difficulties. He is a retired professional football player. He denies numbness/tingling, bowel/bladder dysfunction, or a family history of this problem. EMG/NCS reveals normal sensory nerve action potentials (SNAPs) and compound muscle action potentials (CMAPs) in 3 limbs. Needle exam reveals long-duration, large amplitude motor unit action potentials (MUAPs) with decreased recruitment and 2+ fibrillations in 3 limbs. Which of the following treatments is most likely appropriate? ARiluzole BNusinersen CAntitoxin DCorticosteroids
Answer: A
Explanation:
• This patient’s presentation and EMG findings are classic for ALS (amyotrophic lateral sclerosis). This is the death of anterior horn cells due to a not-yet clearly defined cause.
• It has been associated with a professional athletics history.
• Recall that anterior horn cells are entirely separate from sensory neurons, and, thus, the SNAPs of these patients will be normal.
• CMAPs can be normal vs. abnormal in these patients.
• EMG shows a “neuropathic” pattern of MUAPs as described.
• Riluzole has been shown to prolong survival in ALS patients.
• Rehabilitation with submaximal exercise is recommended.
• ALS carries a poor prognosis, and most patients experience progressive disability and death within a few years of onset.
• Nusinersen is indicated in patients with Spinal Muscular Atrophy.
Median nerve innervated muscles
- Pronator teres
- Palmaris longus
- Flexor carpi radialis
- Flexor digitorum superficialis
- Flexor digitorum profundus (only the lateral half)
- Flexor pollicis longus
- Pronator quadratus
- 1st & 2nd Lumbricals
- Flexor pollicis brevis (superficial head)
- Abductor pollicis brevis
- Opponens pollicis
Ulnar nerve innervated muscles
- Flexor carpi ulnaris
- Flexor digitorum profundus (medial half)
- Palmaris brevis
- 3rd & 4th Lumbricals
- Interossei
- Adductor pollicis - thenar
- Flexor pollicis brevis (deep head) - thenar
- Abductor digiti minimi - hypothenar
- Opponens digiti minimi - hypothenar
- Flexor digiti minimi - hypothenar
- During an EMG, you decide to stimulate the ulnar nerve at the wrist and record the CMAP (compound muscle action potential) over the first dorsal interosseous (FDI), whose amplitude appears normal. You then stimulate the ulnar nerve at the elbow and notice a significantly decreased amplitude compared to the wrist, even when adjusting for the patient’s skin conditions and stimulator placement. You decide to leave the recording electrode in place on the FDI. Which of the following is the next best step?
A Stimulate the anterior interosseous nerve in the forearm
B Stimulate the ulnar nerve above the elbow
C Stimulate the median nerve at the elbow
D Stimulate the ulnar nerve in the forearm, “inching” along to find the location of conduction block
Answer: C
Explanation:
• The Martin-Gruber anastomosis (MGA) involves median nerve fibers in the forearm crossing over and joining the ulnar nerve in the forearm.
• This means essentially that the median nerve innervates the abductor digiti minimi (ADM) and first dorsal interosseous (FDI), which are ulnar nerve muscles, in addition to innervating its own classic median nerve muscles (abductor pollicis brevis - APB, etc.).
• The ulnar nerve CMAP (compound muscle action potential) when stimulating at the elbow will show a low amplitude when recording over a distal ulnar muscle such as FDI. The ulnar CMAP will be “repaired”/normal if you stimulate the ulnar nerve at the wrist. Thus, it appears that there is a conduction block somewhere in the forearm when there actually is NOT (ulnar nerve conduction block in the mid to distal forearm is also very uncommon).
• When you stimulate the ulnar nerve at the wrist, at this point the median nerve fibers have finally joined the ulnar nerve, so you are finally stimulating all the motor axons that are supplying the ulnar nerve hand muscles.
• When you stimulate the ulnar nerve at the elbow, you are NOT stimulating the median nerve fibers that have yet to contribute to the ulnar innervations, thus you only generate part of the full amplitude, which is what makes it look like there is a conduction block in the ulnar nerve, when in reality there is NOT.
• When suspecting a Martin-Gruber anastomosis, the physician should perform further testing by recording over the ADM or FDI and stimulating the median nerve at the elbow to see if a sizeable CMAP can be generated (this will NOT be the full “normal” CMAP, just a small “bump” that represents the small portion of median nerve axons that are destined to cross over and supply the ADM, whereas the lion’s share of median nerve fibers will innervate the classic median nerve muscles and thus will NOT produce any signal here, as we are recording over the FDI, an ulnar nerve muscle).
• If Martin-Gruber anastomosis (MGA) is present, the small median CMAP amplitude you generate with this will “add up” with the proximal ulnar CMAP to create a full normal-amplitude CMAP, just like the normal CMAP when stimulating the ulnar nerve at the wrist.
In a case of axonotmesis of the median nerve at the wrist on EMG/NCS, 1 month after injury you detect decreased CMAP amplitude proximally and distally to the site of injury in addition to decreased recruitment. 2 years later, which of the following findings would you reasonably expect to discover?
A Decreased CMAP amplitude proximally and distally
B Normal CMAP amplitude distally, but not proximally
C Normal CMAP amplitude proximally, but not distally
D Normal CMAP amplitude proximally and distally
Answer: D
Explanation:
• In axonotmesis, even though the axons have died due to crush/stretch injury (leading to decreased CMAP distally and proximally) the epineurium is still intact, which will serve as a guide path for the axons to regenerate along and ultimately find their target muscle fibers again.
• Thus, months to years later, you may detect a repaired, normal CMAP due to axonal regeneration.
You are reviewing EMG/NCS findings. You note abnormal superficial fibular and sural SNAPs (sensory nerve action potentials), normal medial and lateral plantar nerve SNAPs, and abnormal CMAP to the EDB (compound muscle action potential to extensor digitorum brevis). The needle EMG results demonstrate decreased recruitment in tibialis anterior (TA), EDB, and fibularis longus, with normal activity in abductor hallucis, gastrocnemius, semimembranosus, biceps femoris, rectus femoris, tensor fascia lata, and lumbar paraspinals. Which of the following is the most likely diagnosis?
A Sciatic neuropathy
B Superficial fibular neuropathy
C Common fibular neuropathy
D Deep fibular neuropathy
Answer: C
Explanation:
• Common fibular neuropathy is the best answer.
• Deep fibular neuropathy would spare the fibularis longus (innervated by superficial fibular nerve).
• Superficial fibular neuropathy would spare the extensor digitorum brevis and tibialis anterior (innervated by deep fibular nerve).
• Sciatic neuropathy would show abnormalities in gastrocnemius, abductor hallucis, and plantar SNAPs potentially, as well as potentially hamstring muscles.
Which of the following can cause an ulnar neuropathy?
A Arcade of Frohse
B Arcade of Struthers
C Ligament of Struthers
D Bicipital aponeurosis
Answer: B
Explanation:
• The Arcade of Struthers is a piece of fascia connecting the brachialis to the triceps, and the ulnar nerve can become entrapped here.
• The Bicipital aponeurosis and Ligament of Struthers cause median neuropathy at the elbow.
• The Arcade of Frohse causes posterior interosseous neuropathy (a branch of radial nerve).
A patient with weakness presents for repetitive nerve stimulation (RNS). You decide to evaluate the compound muscle action potential (CMAP) of the abductor digiti minimi (ADM). On routine studies, you notice an abnormally low amplitude of the CMAP. During RNS while stimulating the muscle at a rate of 2 Hz, you notice a 20% decrement in the CMAP amplitude when comparing the 1st and 4th waveforms. However, during RNS while stimulating the muscle at a rate of 50 Hz, you notice a surge in the CMAP amplitude, increasing its size by 300%. Which of the following diseases do you suspect?
A Amyotrophic lateral sclerosis (ALS)
B Lambert-Eaton Myasthenic Syndrome (LEMS)
C Myasthenia Gravis (MG)
D Botulism
Answer: B
Explanation:
• Lambert-Eaton Myasthenic Syndrome (LEMS) is due to antibodies against presynaptic calcium channels, and presents with proximal muscle weakness that improves with exercise.
○ LEMS is also commonly secondary to a paraneoplastic process brought on by small cell lung carcinoma (malignant growth of cells).
○ Treatment involves Rehabilitation, Corticosteroids, Anticancer therapy, IVIG/Plasmapheresis.
• Myasthenia gravis (MG) is due to antibodies against postsynaptic neuromuscular junction (NMJ) acetylcholine receptors.
○ Classically symptoms (proximal muscle weakness) worsen with exercise, as the day progresses, and are associated with diplopia.
• Botulism is the final NMJ disease to know, and it is due to inhibition of presynaptic acetylcholine vesicle release into the synapse by botulinum toxin.
• All three of these NMJ diseases can be studied using RNS.
• During low-rate RNS (repetitive nerve stimulation) (2-3 Hz), all of them will show a CMAP decrement by at least 10% when comparing the 1st and 4th waveforms.
• During high-rate RNS (reptitie nerve stimulation) (10-50 Hz) all of them will show a CMAP amplitude increase (CMAP repair), but Lambert-Eaton Myasthenic Syndrome alone will show a massive increase compared to the other two diseases, and can even increase by 300%, which the other diseases simply cannot perform.
• High-rate RNS is one way to determine if the patient is suffering from Lambert-Eaton Myasthenic Syndrome vs. Myasthenia gravis especially.
Which of the following muscles does not receive its innervation from the lateral cord of the brachial plexus?
A Flexor carpi ulnaris
B Pronator teres
C Flexor carpi radialis
D Biceps brachii
Answer: A
Explanation:
• Biceps brachii, flexor carpi radialis, and pronator teres all receive lateral cord innervation. Flexor carpi ulnaris receives medial cord innervation.
Raising the low frequency filter during NCS (nerve conduction studies) will cause which of the following?
A No effect
B Increased amplitude
C Prolonged peak latency
D Shortened peak latency
Answer: D
Explanation:
• Raising the low frequency filter will shorten the peak latency and decrease the amplitude.
A 23 year-old male sustained an injury while playing soccer 2 weeks ago. He presents for an EMG evaluation due to foot drop. X-rays of the right lower limb are negative. On exam, he demonstrates intact lower limb strength except for 3+/5 right ankle dorsiflexion. Tinel at the fibular head is positive for reproduction of numbness and tingling he is experiencing. Nerve conduction studies demonstrate normal sural sensory nerve action potential (SNAP), prolonged latency of the superficial fibular SNAP, and normal compound muscle action potential (CMAP) of the tibialis anterior (TA) when stimulating below the fibular head. However, when stimulating within the popliteal fossa, the TA CMAP amplitude drops 50% compared to the below fibular head stimulation site. Needle EMG of the TA and extensor digitorum brevis (EDB) reveals decreased recruitment. Needle EMG of remaining muscles is normal. Which of the following is the most appropriate response to these findings?
A MRI is recommended
B Ultrasound-guided intervention is recommended
C Surgical opinion should be sought
D Prognosis for recovery is good
Answer: D
Explanation:
• This patient’s results demonstrate neurapraxia of the common fibular nerve, likely due to some physical injury sustained during the soccer match.
• Neurapraxia can be differentiated from axonotmesis (axon loss due to crush/stretch injury) and neurotmesis (axon loss due to complete nerve transection) due to the normal CMAPs present below the level of injury at 2 weeks out from injury.
• There is also the lack of active denervation (fibrillations and positive sharp waves) that suggests neurapraxia rather than axon loss.
• Neurapraxia, you recall, manifests as a conduction block, as in this case (normal amplitude CMAP distal to the lesion, decreased amplitude CMAP proximal to the lesion).
• Neurapraxia/conduction block represents a focal demyelination event; thus the axons are intact, and all that is required is remyelination for the CMAP, recruitment, and patient’s strength to recover.
• If this were axon loss, the CMAP amplitude would also be decreased distally at this point (2 weeks; recall that within ~10 days Wallerian degeneration is complete for both sensory and motor fibers); thus, the intact distal CMAP suggests the axons are alive and healthy, and just awaiting remyelination.
• Thus, this patient’s prognosis for spontaneous recovery is good. Thus, surgery would be inappropriate, MRI is unnecessary, and US-guided intervention is unnecessary.
The first sign of Guillain Barre Syndrome on electrodiagnostic studies is which of the following?
A Prolonged M wave
B Prolonged A wave
C Prolonged F wave
D Prolonged H reflex
Answer: C
Explanation:
• Prolonged or absent F waves are the first sign of GBS on EDX studies.
Which of the following muscles is not a shoulder adductor?
A Teres minor
B Teres major
C Latissimus dorsi
D Pectoralis major
Answer: A
Explanation:
All of the above are shoulder adductors, except the teres minor, which is part of the rotator cuff group and is an external rotator.
Which of the following muscles is innervated by the listed neural pathway? S1, S2; sciatic nerve; tibial nerve; medial plantar nerve.
A Flexor digitorum longus (FDL)
B Flexor hallucis brevis (FHB)
C Abductor digiti quinti pedis (ADQP)
D Flexor hallucis longus (FHL)
Answer: B
Explanation:
• The Flexor hallucis brevis (FHB) and the Abductor hallucis brevis (AHB) are medial plantar nerve-innervated.
• The Flexor hallucis longus (FHL) and Flexor digitorum longus (FDL) are tibial nerve-innervated.
• The Abductor digiti quinti pedis (ADQP) is lateral plantar nerve-innervated.
The purpose of EMG/nerve conduction studies is to diagnose disorders of which of the following?
A Resident’s EMG knowledge base
B Musculoskeletal system
C Peripheral nervous system
D Central nervous system
Answer: C
Explanation:
• The purpose of EMG/NCS is to diagnose peripheral nervous system diseases.
• It tells us nothing of the central nervous system, other than possibly poor activation of muscles.
• Despite how painful learning EMGs can be, its purpose is not to torture residents.
A patient presents with deep fibular neuropathy. Which of the following areas of the foot do you expect to demonstrate sensory abnormalities?
A 5th webspace, sparing the dorsum of the foot
B 1st webspace, sparing the dorsum of the foot
C Dorsum of foot, sparing the 5th webspace
D Dorsum of foot, sparing the 1st webspace
Answer: A
Explanation:
• Deep fibular nerve innervates the skin between the 1st and 2nd toes (the 1st webspace).
• Superficial fibular nerve innervates the skin over the entire dorsum of the foot, except the 1st webspace (which is deep fibular nerve territory).
A trauma results in complete severing of the median nerve at the elbow. Immediate EMG/NCS reveals absent CMAP proximally, and normal CMAP distally. Which of the following is the most likely diagnosis?
A Conduction block
B Neurotmesis
C Neurapraxia
D Axonotmesis
Answer: B
Explanation:
• Neurotmesis is the severing (transection) of a nerve all the way through the epineurium, due to trauma.
• Initially we see an absent CMAP proximally and normal CMAP distally.
• Once Wallerian degeneration is complete (roughly 5 days for motor fibers), we see absent CMAP both distally and proximally to the site of injury.
A 47 year-old male presents to your musculoskeletal clinic with complaints of 3 months of left shoulder pain. He works in the post office handling heavy packages. On exam, you note no pain with empty can, and no pain with resisted external or internal rotation of the shoulder. When abducting the arm 90 degrees and flexing the elbow 90 degrees, and then performing resisted external rotation of the shoulder, this reproduces the patient’s pain. What is the innervation of the muscle being tested?
A Upper subscapular nerve
B Axillary nerve
C Lower subscapular nerve
D Suprascapular nerve
Answer: B
Explanation:
• The physical exam maneuver described is how one isolates and tests the teres minor, which is innervated by C5,C6, upper trunk, posterior cord, axillary nerve.
• The suprascapular nerve innervates the supraspinatus and infraspinatus, and these muscles are not tested in the way this question describes.
• The upper and lower subscapular nerves innervate the subscapularis and teres major (lower subscapular nerve → teres major), tested differently from how this question describes.
A patient presents with left foot drop. On EMG/NCS, you note normal superficial fibular and sural nerve SNAPs (sensory nerve action potentials). EMG reveals 3+ positive sharp waves and decreased recruitment in the tibialis anterior (TA), extensor digitorum longus (EDL), extensor hallucis longus (EHL), and extensor digitorum brevis (EDB). EMG of the fibularis longus, abductor hallucis (AH), medial gastrocnemius, hamstrings, rectus femoris, thigh adductors, tensor fascia lata, and lumbar paraspinals is normal. Which of the following is the most likely diagnosis?
A Deep fibular neuropathy
B L4 radiculopathy
C Distal sciatic neuropathy
D Superficial fibular neuropathy
Answer: A
Explanation:
• Deep fibular neuropathy is the best answer.
• Superficial fibular neuropathy would affect fibularis longus and superficial fibular SNAP, and spare all the affected muscles in this question.
• Distal sciatic neuropathy would affect gastrocnemius and AH, as well as fibularis longus, and potentially superficial fibular SNAP.
• L4 radiculopathy would indeed show normal SNAPs, but would also be expected to affect other muscles receiving L4 innervation, such as rectus femoris, hamstrings, and thigh adductors.
Duchenne muscular dystrophy (DMD) usually begins with weakness in which of the following muscle groups?
A Knee extensors
B Plantarflexors
C Hip extensors
D Neck flexors
Answer: D
Explanation:
• Duchenne Muscular Dystrophy (DMD)’s earliest signs of muscle weakness are classically found in the neck flexors.
The sternocleidomastoid (SCM) shares its innervation with which of the following muscles?
A Splenius capitis
B Rhomboid major
C Rhomboid minor
D Trapezius
Answer: D
Explanation:
• The SCM and trapezius are innervated by C3, C4; spinal accessory nerve.
• The rhomboids are innervated by C4, C5; dorsal scapular nerve.
• It’s not important for you to know splenius capitis’ innervation, but it’s not the spinal accessory nerve.
A patient’s left upper limb EMG/NCS results are as follows. Routine median, ulnar, and radial sensory nerve conduction studies are normal. EMG reveals decreased recruitment and 4+ fibrillations in triceps, extensor indicis proprius, abductor pollicis brevis, and first dorsal interosseous, but normal resting activity and recruitment in deltoid, biceps, brachioradialis, and pronator teres. Which of the following is the most likely diagnosis?
A C8 radiculopathy
B C7 radiculopathy
C C6 radiculopathy
D C5 radiculopathy
Answer: A
Explanation:
• All muscles supplied by the C8 nerve root are affected, but those not involving the C8 nerve are spared; thus, C8 radiculopathy is the best answer.
• Please refer to the innervation chart at the beginning of the Upper and Lower Extremity Peripheral Nervous System Diseases chapters for a detailed innervation guide.
While examining a patient you notice that their right scapula sits more medially than the left scapula. Needle EMG would most likely reveal abnormalities of musculature belonging to which nerve?
A Thoracodorsal nerve
B Spinal accessory nerve
C Dorsal scapular nerve
D Long thoracic nerve
Answer: D
Explanation:
• The two nerves associated with winged scapula (this patient has a medially winged scapula) are:
• Long thoracic nerve (innervates the serratus anterior -> protracts scapula): injury can cause a medially winged scapula
• Spinal accessory nerve (innervates the trapezius -> retracts scapula): injury can cause a laterally winged scapula
• Dorsal scapular nerve (innervates the rhomboids -> retracts scapula).
• Thoracodorsal nerve (innervates the latissimus dorsi): adduct, internally rotate and extend arm
While performing a nerve conduction study (NCS) you apply current to the nerve and detect a small amplitude. You then move distally on the limb and apply current again to the nerve. To your surprise, the amplitude is normal. What is the most likely explanation for this finding?
A Total axonal loss
B Partial conduction block
C Total conduction block
D Partial axonal loss
Answer: B
Explanation:
• Axonal loss is seen with decreased amplitude throughout an entire nerve’s length. EMG will show decreased recruitment in these cases.
• Conduction block is seen with proximally reduced amplitude, but stimulating distally beyond the spot of conduction block can demonstrate a normal “repaired” amplitude.
Which of the following nerves is associated with the spinoglenoid notch?
A Thoracodorsal nerve
B Suprascapular nerve
C Axillary nerve
D Dorsal scapular nerve
Answer: B
Explanation:
• The suprascapular nerve innervates the supraspinatus, then passes through the spinoglenoid notch to innervate the infraspinatus.
• This is an important anatomical consideration when performing an EMG involving both supraspinatus and infraspinatus.
• The axillary nerve passes through the quadrilateral space of the axilla.
Which of the following correctly states the innervation of the flexor digitorum superficialis of the forearm?
A C6, C7, upper and middle trunk, medial and lateral cord, median nerve
B C7, C8, middle and lower trunk, medial and lateral cord, median nerve, AIN (ant. interosseous nerve)
C C7, C8, T1, middle trunk, medial cord, median nerve
D C7, C8, middle and lower trunk, medial and lateral cord, median nerve
Answer: D
Explanation:
“C7, C8, middle and lower trunk, medial and lateral cord, median nerve” correctly states the FDS innervation.
When a muscle recruits its first motor unit during initial contraction, it tends to fire at \_\_\_\_\_ Hz, and subsequent motor units are recruited for every \_\_\_\_\_\_ Hz increase in firing rate. A 10, 15 B 5, 5 C 10, 10 D 5, 10
Answer: B
Explanation:
• The initial motor unit is recruited at 5 Hz.
• Every 5 Hz an additional motor unit is added to the recruitment pattern.
• Thus, your EMG screen should at some point show you 4 motor units firing at once with gradually increased muscle contraction by the patient: these units will be firing at 20, 15, 10, 5 Hz respectively.
During an upper limb EMG/NCS study, you detect prolonged SNAP latency to digit 2, digit 5, and the dorsal ulnar cutaneous nerve. EMG reveals decreased recruitment to the abductor digiti minimi and flexor digitorum profundus to digits 4 and 5. Which of the following is most likely to narrow down the diagnosis?
A Needle EMG sampling of flexor carpi ulnaris (FCU)
B Testing the lateral antebrachial cutaneous nerve SNAP
C Comparing the DUC between left and right sides
D Testing the medial antebrachial cutaneous nerve SNAP
Answer: D
Explanation:
• These EMG/NCS results suggest either ulnar neuropathy at the elbow or medial cord brachial plexopathy.
• The medial antebrachial cutaneous nerve (MAC) branches off the medial cord of the brachial plexus to supply cutaneous innervation to the medial forearm just before the medial cord continues down to form the ulnar nerve.
• Thus, an abnormal MAC would indicate medial cord plexopathy (or lower trunk plexopathy), indicating that the nerve problem is somewhere proximal to the ulnar nerve, NOT at the ulnar nerve.
• However, a normal MAC would indicate that the medial cord of the plexus is intact, thus localizing the problem distally (likely the ulnar nerve at the elbow in this case).
• Comparing the dorsal ulnar cutaneous (DUC) nerve between both sides is NOT helpful, as we already know that ours being studied is abnormal.
• Obtaining the lateral antebrachial cutaneous SNAP (arises as a continuation of the musculocutaneous nerve from the lateral cord of the plexus) will NOT inform us on the status of the medial cord of the plexus, thus making this less helpful to us in this case.
• Finally, needling the flexor carpi ulnaris (FCU) may show abnormalities in this muscle, which could be caused by medial cord plexopathy or ulnar neuropathy at the elbow; thus, this would NOT help us narrow our diagnosis.
Years following a neurotmesis injury in the forearm, what is the most reasonable expectation on EMG/NCS?
A Equally any of the above
B Normal CMAP
C “Repaired” CMAP
D Absent CMAP
Answer: D
Explanation:
• Neurotmesis is the complete transection of a nerve.
• Thus, axons have NO connective tissue nerve path through which they may find their former muscle fibers, and the CMAP most likely will NOT be normal or partially repaired.
A Martin-Gruber anastomosis is an anatomic variant consisting of which of the following nerve findings?
A Ulnar to median anastomosis
B Median to posterior interosseous anastomosis
C Ulnar to anterior interosseous anastomosis
D Median to ulnar anastomosis
Answer: D
Explanation:
• Martin-Gruber anastomosis involves median nerve fibers in the forearm crossing over and joining the ulnar nerve in the forearm.
• This means essentially that the median nerve innervates the abductor digiti minimi (ADM) and first dorsal interosseous (FDI), which are ulnar nerve muscles, in addition to innervating its own classic median nerve muscles (abductor pollicis brevis - APB, etc.).
• The ulnar nerve CMAP (compound muscle action potential) when stimulating at the elbow will show a low amplitude than when recording over a distal ulnar muscle such as FDI.
• The ulnar CMAP will be “repaired”/normal if you stimulate the ulnar nerve at the wrist.
• Thus, it appears that there is a conduction block somewhere in the forearm when there actually is NOT.
• When you stimulate the ulnar nerve at the wrist, at this point the median nerve fibers have finally joined the ulnar nerve, so you are finally stimulating all the motor axons that are supplying the ulnar nerve hand muscles.
• When you stimulate the ulnar nerve at the elbow, you are NOT stimulating the median nerve fibers that have yet to contribute to the ulnar innervations, thus you only generate part of the full amplitude, which is what makes it look like there is a conduction block in the ulnar nerve, when in reality there is NOT.
• When suspecting a Martin-Gruber anastomosis (MGA), the physician should perform further testing by recording over the ADM or FDI and stimulating the median nerve at the elbow to see if a sizeable CMAP can be generated (this will NOT be the full “normal” CMAP, just a small “bump” that represents the small portion of median nerve axons that are destined to cross over and supply the ADM, whereas the lion’s share of median nerve fibers will innervate the classic median nerve muscles and thus will NOT produce any signal here, as we are recording over the FDI, an ulnar nerve muscle).
• If MGA is present, the small CMAP amplitude you generate with this will “add up” with the proximal ulnar CMAP to create a full normal-amplitude CMAP, just like the normal CMAP when stimulating the ulnar nerve at the wrist.
What does a polyphasic potential represent during an EMG?
A Active reinnervation
B Prior denervation
C Prior reinnervation
D Active denervation
Answer: A
Explanation:
• Polyphasic potentials represent ongoing reinnervation due to collateral sprouting of existing axons.
• The polyphasic property arises due to non-uniform myelination of these collateral sprouts during this early reinnervation stage.
Which of the following muscles is NOT innervated by the anterior interosseous nerve?
A Flexor digitorum superficialis
B Flexor digitorum profundus
C Flexor pollicis longus
D Pronator quadratus
Answer: A
Explanation:
• FDS is innervated directly by the median nerve, NOT the anterior interosseous nerve (which arises from the median nerve).
An EMG potential is described as polyphasic if it crosses the baseline a minimum of how many times?
A 6
B 5
C 4
D 3
Answer: B
Explanation:
Polyphasic potentials are defined as a baseline crossing of 5 or more times
Neurapraxia can be defined as which of the following?
A None of these answers is correct
B Complete severance of a nerve through the epineurium, causing paralysis of “downstream” muscles
C Focal pressure on a nerve, leading to focal demyelination and conduction block
D Nerve injury leading to axonal loss with the epineurium still intact
Answer: C
Explanation:
• “Focal pressure on a nerve, leading to focal demyelination and conduction block” describes neurapraxia, which is essentially a focal conduction block.
• This can become remyelinated over 2-3 weeks, resolving the conduction block.
• The pathologic compression stimulus must be removed for this healing to occur, however.
A 60 year-old female presents with proximal hip and shoulder weakness, periorbital erythematous rash, and erythematous papules over her metacarpophalangeal (MCP) and interphalangeal (IP) joints of the hands. Which of the following EMG findings is most likely present in this patient?
A Decreased amplitude sensory nerve action potentials (SNAPs)
B Giant motor unit action potentials (MUAPs)
C Decreased recruitment
D Early/increased recruitment
Answer: D
Explanation:
• This patient presents with classic dermatomyositis (proximal muscle weakness with heliotrope rash and Gottron papules).
• This is a myopathic disease; thus, the EMG will show signs of myopathy:
○ Short-duration
○ Small amplitude MUAPs with
○ Early/Increased recruitment
• Decreased recruitment is found in nerve disorders, not muscle disease.
• Giant MUAPs are found in post-polio syndrome.
• Decreased SNAP amplitudes can be found in any sensory nerve disease that affects axons.
During an EMG, you decide to stimulate the ulnar nerve at the elbow and record the CMAP (compound muscle action potential) over the abductor digiti minimi (ADM). You then stimulate the ulnar nerve at the wrist and notice a much higher amplitude at the wrist than when stimulating at the elbow. Which of the following is the most likely etiology of these findings?
A Axonotmesis
B Martin-Gruber anastomosis
C Conduction block
D Riche-Cannieu anastomosis
Answer: B
Explanation:
• The Martin-Gruber anastomosis involves median nerve fibers in the forearm crossing over and joining the ulnar nerve in the forearm. This means essentially that the median nerve innervates the abductor digiti minimi (ADM) and first dorsal interosseous (FDI), which are ulnar nerve muscles, in addition to innervating its own classic median nerve muscles (abductor pollicis brevis - APB, etc.).
• The ulnar nerve CMAP (compound muscle action potential) when stimulating at the elbow will show a low amplitude when recording over a distal ulnar muscle such as FDI.
• The ulnar CMAP will be “repaired”/normal if you stimulate the ulnar nerve at the wrist. Thus, it appears that there is a conduction block somewhere in the forearm when there actually is not (ulnar nerve conduction block in the mid to distal forearm is also very uncommon).
• When you stimulate the ulnar nerve at the wrist, at this point the median nerve fibers have finally joined the ulnar nerve, so you are finally stimulating all the motor axons that are supplying the ulnar nerve hand muscles.
• When you stimulate the ulnar nerve at the elbow, you are not stimulating the median nerve fibers that have yet to contribute to the ulnar innervations, thus you only generate part of the full amplitude, which is what makes it look like there is a conduction block in the ulnar nerve, when in reality there is not.
• When suspecting a MGA, the physician should perform further testing by recording over the ADM or FDI and stimulating the median nerve at the elbow to see if a sizeable CMAP can be generated (this will not be the full “normal” CMAP, just a small “bump” that represents the small portion of median nerve axons that are destined to cross over and supply the ADM, whereas the lion’s share of median nerve fibers will innervate the classic median nerve muscles and thus will not produce any signal here, as we are recording over the FDI, an ulnar nerve muscle).
• If MGA is present, the small CMAP amplitude you generate with this will “add up” with the proximal ulnar CMAP to create a full normal-amplitude CMAP, just like the normal CMAP when stimulating the ulnar nerve at the wrist.
A 45 year-old female presents with 3 months of right foot drop and leg pain. On exam, tinel at the fibular head is positive. Nerve conduction studies of the right lower limb (NCS) reveal prolonged latency of sural and superficial fibular SNAPs (sensory nerve action potential) and decreased amplitude of extensor digitorum brevis (EDB) CMAP (compound muscle action potential). EMG reveals decreased recruitment of tibialis anterior (TA), EDB, abductor hallucis (AH), fibularis longus, and semitendinosus. EMG of lumbar paraspinals, gluteus maximus, tensor fascia lata (TFL), rectus femoris, and thigh adductors is normal. Which of the following is the most likely diagnosis?
A L5 radiculopathy
B Proximal sciatic neuropathy
C Distal sciatic neuropathy
D Common fibular neuropathy
Answer: B
Explanation:
• Proximal sciatic neuropathy is the best choice, as all sciatic nerve-innervated muscles (some hamstrings and the gastroc/soleus are untested) are affected on EMG, as well as both tibial and fibular SNAPs being affected as well, indicating that most parsimonious explanation is a proximal sciatic neuropathy.
• A distal sciatic neuropathy, such as at the knee, would spare the hamstrings, which are affected in this case.
• A radiculopathy would show normal SNAPs (abnormal in this case).
• Common fibular neuropathy would spare the hamstrings and the abductor hallucis, both of which are affected in this case.
Normal upper and lower extremity conduction velocities are at least which of the following, respectively, in meters per second?
A 50, 50
B 50, 40
C 40, 50
D 40, 40
Answer: B
Explanation:
• Normal upper and lower limb CV is at least 50 m/s and 40 m/s respectively.
During a diagnostic ultrasound scan, you notice a structure that appears like a honeycomb. Which of the following are you most likely viewing?
A Tendon
B Nerve
C Vein
D Artery
Answer: B
Explanation:
• On ultrasound, in a short axis view (cross-sectional view), a nerve looks like a honeycomb.
• Veins and arteries look like hollow (dark/anechoic) tubes that are compressible by the transducer.
• A tendon appears more uniformly hyperechoic (bright) than a nerve.
A patient’s right lower limb EMG/NCS results are as follows. Routine fibular and tibial motor/sensory nerve conduction studies are normal. EMG reveals decreased recruitment and polyphasic potentials in tensor fascia lata, rectus femoris, adductor longus, semimembranosus, and tibialis anterior, but normal activity in short head of biceps femoris, fibularis longus, gastrocnemius, and abductor hallucis. Which of the following is the most likely diagnosis? AS1 radiculopathy BL5 radiculopathy CL4 radiculopathy DL3 radiculopathy
Answer: C
Explanation:
• All muscles receiving some degree of L4 innervation are affected here, but all those without L4 innervation are spared.
• Note that the short head of biceps femoris is innervated by L5-S1, common fibular division of sciatic nerve, thus differentiating it from the medial hamstrings and long head of biceps femoris, which have L4-L5-S1, tibial division of sciatic nerve innervation.
Note also that typically an S1 radiculopathy question will refer to an abnormal H-reflex as partial evidence of an S1 radiculopathic process.
A 66 year-old male develops right leg pain and weakness following a hospital stay for acute coronary syndrome requiring cardiac stenting. On exam he demonstrates isolated knee extension weakness. On EMG/NCS he demonstrates abnormal CMAP (compound muscle action potential) to the rectus femoris. Needle EMG reveals decreased recruitment and 1+ fibrillations in the vastus medialis. In order to cinch the diagnosis, you decide to perform additional studies, and expect to find which of the following findings? SNAP: sensory nerve action potential.
AProlonged latency of saphenous SNAP
BAbnormal EMG activity in adductor longus
CAbnormal EMG activity in extensor digitorum brevis
DDecreased amplitude of sural SNAP
Answer: A
Explanation:
• This patient presents with femoral neuropathy due to cardiac catheter trauma (inserting the catheter into the femoral artery - next to the femoral nerve).
• The femoral nerve terminates as the saphenous nerve, supplying skin innervation to the medial leg below the knee.
• Thus, the saphenous nerve SNAP being abnormal would nicely complete the diagnosis of femoral neuropathy in this patient.
Regarding the dorsal and palmar interossei of the hand, which of the following statements is true?
AThey share the same innervation
BThey have ulnar and anterior interosseous nerve innervation, respectively
CThey are not routinely needled during an EMG study
DThey have ulnar and median nerve innervation, respectively
Answer: A
Explanation:
• The dorsal and palmar interossei of the hand are all innervated by the ulnar nerve.
• The first dorsal interosseous (FDI) is routinely needled in an EMG study as a valuable, accessible ulnar nerve-innervated muscle in the hand.
You are performing an EMG and decide to advance the needle into a muscle at rest when you hear what sounds like a “divebomber”. Which of the following is the most likely diagnosis? AAll of the listed choices are correct BHyperkalemic periodic paralysis CMyotonia congenita DMyotonic dystrophy
Answer: A
Explanation:
• A divebomber sound is classic for myotonic discharges. This can be seen on the screen as a steadily decreasing amplitude as the muscle fiber continues to fire.
• Essentially anything with “myotonia” in its name can demonstrate myotonic discharges on EMG, as can hyperkalemic periodic paralysis and acid maltase deficiency.
A 58 year-old female complains of sudden-onset severe shoulder pain for 2 weeks, which then improves and is followed by progressive onset shoulder weakness. She denies trauma. Shoulder x-ray and MRI are negative. On exam she has weakness in shoulder abduction. EMG/NCS reveals decreased recruitment and +2 positive sharp waves in the supraspinatus and infraspinatus. Which of the following is the most reasonable advice you should give to this patient?
A All of the listed answer choices are equally reasonable
B Repeat EMG within 6 months is not typically useful
C Nerve transposition should be considered early in the course of the disease
D Most cases self-resolve within 1-2 years
Answer: D
Explanation:
• This patient presents with classic Parsonage-Turner Syndrome (neuralgic amyotrophy, brachial neuritis, idiopathic brachial plexopathy).
• This typically presents as sudden shoulder pain for 2 weeks which gives way to weakness from atrophy.
• Suprascapular (this case), long thoracic, axillary, musculocutaneous, anterior & posterior interosseous nerves are most commonly affected.
○ It is a multifocal, immune-mediated inflammatory process that involves the peripheral nerves.
○ Most lesions are axonal. Those caused by demyelination carry a better prognosis. Motor axons are mainly affected.
• Serial EMGs are useful for prognosis, and most cases self-resolve within 1-2 years after onset.
• Early surgical options would NOT be indicated, as most cases self-resolve.
• Parsonage-Turner Syndrome (PTS) typically begins following a viral illness, surgery, anesthesia, rheumatic diseases such as connective tissue disorders (i.e., Ehlers-Danlos syndrome), SLE, temporal arteritis, and polyarteritis nodosa. Trauma to the shoulder girdle and stressful exercise are other determining factors.
• Other sources include immunizations (tetanus toxoid and antitoxtin; diphtheria, pertussis, tetanus (DPT) vaccine), smallpox, swine flu, pregnancy, childbirth, radiation therapy, lumbar puncture, pneumoencephalogram, radiologic contrast dye, allergy desensitization.
Which of the following involves the postsynaptic portion of the neuromuscular junction?
A Myasthenia Gravis (MG)
B Post-Polio Syndrome
C Botulism
D Lambert-Eaton Syndrome (LEMS)
Answer: A
Explanation:
• Lambert-Eaton Syndrome (LEMS) and botulism are presynaptic neuromuscular junction (NMJ) disorders.
• Post-Polio Syndrome involves the burning out and subsequent death of anterior horn cells that survived a patient’s remote history of polio.
• Myasthenia Gravis (MG) is truly a postsynaptic NMJ disease involving antibodies against the acetylcholine receptor on the postsynaptic membrane.
You are performing an EMG on a patient with hand numbness. NCS reveals non-recordable sensory nerve action potential (SNAP) to digit 2, and normal SNAP to digit 5. The compound motor action potential (CMAP) to the abductor pollicis brevis (APB) demonstrates decreased amplitude and prolonged latency. Needle EMG to the APB reveals 1+ fibrillations and positive sharp waves and mildly decreased recruitment. EMG of the remaining muscles, including the pronator teres, is normal. Which of the following is the next best step?
A Ibuprofen, repeat EMG in 6 months to monitor progression
B Hand surgeon referral
C Corticosteroid injection
D Wrist bracing
Answer: B
Explanation:
• This patient with absent median nerve SNAP, reduced median CMAP amplitude, prolonged motor latency, and active denervation to the APB (median nerve-innervated muscle, active denervation as evidenced by fibrillations and positive sharp waves on EMG) should be referred to a hand surgeon for carpal tunnel release.
• This case represents severe CTS due to active denervation and decreased CMAP amplitude, together representing ongoing axon loss. (moderate to severe cases are usually most appropriate for surgeon referral).
• Wrist bracing and ibuprofen with EMG monitoring is appropriate for mild cases (prolonged SNAP latency only). Injection is appropriate for mild-moderate cases that fail to improve with conservative treatment (moderate CTS: prolonged SNAP and CMAP latency but normal CMAP amplitude).
A 23 year-old male sustained an injury while playing soccer 2 weeks ago. He presents for an EMG evaluation due to foot drop. X-rays of the right lower limb are negative. On exam, he demonstrates intact lower limb strength except for 3+/5 right ankle dorsiflexion. Tinel at the fibular head is positive for reproduction of numbness and tingling he is experiencing. Nerve conduction studies demonstrate normal sural sensory nerve action potential (SNAP), prolonged latency of the superficial fibular SNAP, and normal compound muscle action potential (CMAP) of the tibialis anterior (TA) when stimulating below the fibular head. However, when stimulating within the popliteal fossa, the TA CMAP amplitude drops 50% compared to the below fibular head stimulation site. Needle EMG of the TA and extensor digitorum brevis (EDB) reveals decreased recruitment. Needle EMG of remaining muscles is normal. Which of the following is the most appropriate response to these findings?
A MRI is recommended
B Ultrasound-guided intervention is recommended
C Surgical opinion should be sought
D Prognosis for recovery is good
Answer: D
Explanation:
• This patient’s results demonstrate neurapraxia of the common fibular nerve, likely due to some physical injury sustained during the soccer match. Neurapraxia can be differentiated from axonotmesis (axon loss due to crush/stretch injury) and neurotmesis (axon loss due to complete nerve transection) due to the normal CMAPs present below the level of injury at 2 weeks out from injury.
• There is also the lack of active denervation (fibrillations and positive sharp waves) that suggests neurapraxia rather than axon loss.
• Neurapraxia, you recall, manifests as a conduction block, as in this case (normal amplitude CMAP distal to the lesion, decreased amplitude CMAP proximal to the lesion).
• Neurapraxia/conduction block represents a focal demyelination event; thus the axons are intact, and all that is required is remyelination for the CMAP, recruitment, and patient’s strength to recover. If this were axon loss, the CMAP amplitude would also be decreased distally at this point (2 weeks; recall that within ~10 days Wallerian degeneration is complete for both sensory and motor fibers); thus, the intact distal CMAP suggests the axons are alive and healthy, and just awaiting remyelination; thus, this patient’s prognosis for spontaneous recovery is good.
• Thus, surgery would be inappropriate, MRI is unnecessary, and US-guided intervention is unnecessary.
Normal motor recruitment follows which of the following principles?
A Type II motor units are recruited before Type 1 motor units
B Both small and large motor units are recruited at essentially equal rates
C The smallest motor units are recruited first
D The largest motor units are recruited first
Answer: C
Explanation:
• Small motor units are recruited before large units.
• Type II motor units are fast twitch, powerful fibers that are recruited with maximal intensity, thus filling the EMG screen with motor units by the time Type II units are recruited.
• Type I: Type I motor units develop a low peak force in a relatively long period of time (60 - 120 ms). Type I motor units are very resistant to fatigue because they’re nourished with an extensive blood supply to maintain aerobic metabolism. Another name for Type I motor units is slow-twitch oxidative, based on the slow tension development time and the use of oxygen. Because they’re fatigue resistant, Type I motor units are the first motor units recruited by the central nervous system when a muscle is activated, and they continue to be recruited as long as the muscle remains active. Type I motor units are well adapted for low-intensity work like maintaining posture. They’re sometimes called tonic motor units because they provide “muscle tone.”
Type II: Type II motor units develop a high peak force in a relatively short period of time (10 - 50 ms). Type II motor units are called fast-twitch motor units because of this quicker response time. Another common name is the phasic motor unit, because Type II motor units are recruited after Type I motor units to provide short bursts, or phases, of higher muscle tension as required.
The supraspinatus and infraspinatus are innervated by which of the following pathways?
A C5, C6 upper trunk, posterior cord, dorsal scapular nerve
B C5, upper trunk, lateral cord, dorsal scapular nerve
C C5, C6, upper trunk, suprascapular nerve
D C5, upper trunk, posterior cord, suprascapular nerve
Answer: C
Explanation:
• “C5, C6, upper trunk, suprascapular nerve” is the correct innervation of supraspinatus and infraspinatus.
Which of the following muscles has the highest innervation ratio?
A Gluteus maximus
B Abductor pollicis brevis
C Levator palpebra
D Pronator teres
Answer: A
Explanation:
• Innervation ratio (IR) refers to the number of muscle fibers innervated by one alpha motor neuron.
• Remember: “huge” muscles have “huge” innervation ratios.
• IR = #muscle fibers per motor neuron.
• In small muscles that require fine control, it makes sense that each muscle fiber “gets more attention” from its alpha motor neuron in order to achieve fine manipulation/control/coordination.
The quadriceps femoris is innervated by which of the following nerve root groups?
A L4, L5, S1
B L3, L4, L5
C L2, L3, L4
D L1, L2, L3
Answer: C
Explanation:
• The quadriceps are innervated by L2, L3, L4 nerve roots. The femoral nerve is the peripheral nerve that innervates the quadriceps.
When listening to a muscle at rest, you see a signal that appears like a normal motor unit action potential (MUAP) and occurs at irregular intervals. What is the proper term for this signal?
A Fasciculation
B Myokymia
C Positive sharp wave
D Fibrillation
Answer: A
Explanation:
• This question describes a fasciculation, which can be seen in normal patients, and classically in ALS patients as well.
• ALS = amyotrophic lateral sclerosis.
A 67 year-old female with a history of facial trauma presents with complaints of crying every time she eats. She denies any actual emotional disturbances. What is the most likely etiology of this problem?
A Synkinesis
B Abnormal R2 response
C Demyelination
D Neurotmesis
Answer: A
Explanation:
• Synkinesis is the inappropriate regeneration of the facial nerve after it is damaged, leading to the nerve reinnervating muscles inappropriately in such a fashion that the patient may end up doing two “facial nerve” activities at once when the patient only means to do one of these.
• For example, blinking and moving their mouth at the same time, or salivating whenever they cry.
A 25 year-old female is involved in a motor vehicle accident. She suffers a left proximal femur fracture and requires orthopedic surgery to repair her left hip. She presents to your inpatient rehabilitation unit 2 weeks later for functional restoration. On exam, you note intact right lower limb strength, intact left hip flexion, knee extension, adduction, internal/external rotation, and abduction strength, but impaired knee flexion, dorsiflexion, and inversion. She has paresthesias in her posterior thigh and anterior shin. What is the most likely diagnosis?
A Tibial and common fibular neuropathies
B Sciatic neuropathy
C Femoral neuropathy
D Lumbosacral plexopathy
Answer: B
Explanation:
• This patient presents with findings concerning for sciatic neuropathy, either as a result of the trauma itself, or the surgical approach (posterior approach places sciatic nerve at risk).
• Proximal sciatic neuropathy will affect essentially all sciatic-innervated muscles, including hamstrings, and all muscles originating at or below the knee. Thus, knee flexion is impaired (hamstrings), dorsiflexion is impaired (common fibular nerve, which arises from sciatic nerve), and inversion is impaired (tibial nerve, which arises from sciatic nerve). Plantarflexion would also be impaired (gastroc/soleus, tibial nerve), but this was not mentioned in the exam.
• Femoral neuropathy would cause impaired knee extension (intact in this patient);
• Lumbosacral plexopathy would cause patchy abnormalities not likely cleanly narrowed down to a single nerve (as in this case).
• Tibial and common fibular neuropathies would indeed cause the abnormalities discussed here, EXCEPT the impaired knee flexion and paresthesias in the posterior thigh imply a proximal sciatic nerve pathology, leading to weak hamstrings.
When compared to a concentric needle electrode, a monopolar needle electrode can be described as which of the following?
A None of these answers is correct
B Overall better than concentric
C Broader “listening” area
D Does not require a separate reference electrode
Answer: C
Explanation:
• Monopolar needles achieve a broader listening area (“listening” to the electrical activity of muscles) than concentric needles, but require a separate surface reference electrode on the skin.
• “Better” is a subjective term with regards to EMG needles. For example, Dr. D’Angelo happens to believe concentric needles are better, as they contain a built-in reference electrode. Taste is subjective!
During an EMG, with the muscle at rest, you decide to advance your needle until you hear a “seashell” sound. What does this sound represent?
A Ephaptic transmission
B Miniature endplate potentials
C Active denervation
D Endplate potentials
Answer: B
Explanation:
• The “seashell” sound is the sound of miniature endplate potentials (MEPPs), which are heard when the needle is very close to endplates, which is a painful needle location for the patient.
A patient attempts to place their hand in their pocket, but their 5th digit sticks out of the pocket while the remaining fingers dive into the pocket as intended. You are an astute physiatrist and notice this immediately. You tell the patient that they have a positive ______ sign.
A Wartenberg
B Allen
C “OK”
D Froment
Answer: A
Explanation:
• The Wartenberg sign is described, indicating ulnar neuropathy (at the wrist or elbow).
• The Froment sign is described as the patient attempting to prevent a piece of paper from being pulled out of their grip, by gripping a piece of paper between their index finger and their thumb with the thumb remaining extended the entire time; a positive Froment sign will show the paper slip out easily due to ulnar nerve muscle weakness, or the patient compensating by flexing their thumb’s interphalangeal joint (via flexor pollicis longus - anterior interosseous nerve).
• The “OK” sign is performed by asking the patient to flex their thumb interphalangeal joint and flex the distal interphalangeal (DIP) joint of the index finger while extending digits 3-5 to make the classic “OK” sign.
• In patients with anterior interosseous neuropathy (AIN-opathy), thumb flexion (flexor pollicis longus) and DIP flexion (flexor digitorum profundus) will be affected, as these are both anterior interosseous nerve functions.
• These patients will essentially keep a straight finger and thumb while pinching them together, instead of flexing these joints properly.
• Note: the Froment sign (ulnar neuropathy) and the “OK” sign (AIN-opathy) are essentially opposite tests of each other! The Allen test is a vascular test not high-yield enough for PM&R physicians to know for boards.
During an upper limb EMG/NCS study you note normal sensory nerve action potentials (SNAPs) to digits 1, 2, and 5. Compound motor action potentials (CMAPs) to the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) are normal. Needle EMG reveals decreased recruitment and abnormal spontaneous activity in the brachialis and biceps, with normal EMG of cervical paraspinals, triceps, brachioradialis, pronator teres, APB, and FDI. Which of the following would also most likely be found in this study?
A Abnormal EMG of the anconeus
B Absent lateral antebrachial cutaneous nerve (LAC) SNAP
C Abnormal CMAP to flexor carpi radialis (FCR)
D Absent CMAP to extensor indicis proprius (EIP)
Answer: B
Explanation:
• This patient presents with findings consistent with musculocutaneous neuropathy. This nerve innervates the coracobrachialis (not discussed here), biceps brachii, and brachialis, hence the abnormal EMG to the biceps and brachialis.
• The musculocutaneous nerve terminates as the lateral antebrachial cutaneous (LAC) nerve; thus, LAC SNAP should be studied and would be expected to be abnormal compared to the contralateral side.
• Absent CMAP to extensor indicis proprius (EIP) could be seen in posterior interosseous neuropathy or a proximal radial neuropathy.
• Radial neuropathy above the humerus midshaft could cause abnormal EMG to the anconeus.
• Abnormal CMAP to the flexor carpi radialis (FCR) could be caused by median neuropathy, but not musculocutaneous neuropathy.
You are performing serial EMGs on a patient. Over time you notice that while he used to demonstrate polyphasic motor unit action potentials (MUAPs) in a particular muscle, on his most recent EMG these polyphasic potentials have been replaced by larger, non-polyphasic potentials. What is the most reasonable explanation for this finding?
A Collateral sprouting
B Myelination
C Demyelination
D Chronic denervation
Answer: B
Explanation:
• Polyphasic potentials represent ongoing reinnervation due to collateral sprouting of existing axons.
• The polyphasic property arises due to non-uniform myelination of these collateral sprouts during this early reinnervation stage.
• Once myelination is complete, the motor unit’s branches all conduct the action potential at essentially the same speed, producing a nice, uniform “roller coaster” bump (uniform-appearing MUAP) rather than the polyphasic, serrated potential seen in unmyelinated collateral sprouts.
You are performing an EMG/NCS on a patient. NCS reveals abnormal sensory nerve action potential (SNAP) to digit 5. Dorsal ulnar cutaneous nerve (DUC) SNAP latency is prolonged. Which of the following is the most likely diagnosis?
A Ulnar neuropathy at the elbow
B Median neuropathy at the wrist
C Ulnar neuropathy at the wrist
D C8 radiculopathy
Answer: A
Explanation:
• In the wrist the dorsal ulnar cutaneous (DUC) nerve innervates the skin of the dorsal ulnar wrist (most reliably the web space between the dorsal 4th and 5th digits, where it is recorded on NCS).
• The DUC does NOT pass through Guyon’s canal.
• If the DUC is normal, but the 5th digit ulnar SNAP is abnormal, the ulnar nerve is being compromised at the wrist, given the normal DUC.
• If the DUC is abnormal, as in this patient, then that means the ulnar nerve compression must be happening somewhere proximal to the wrist, such as the elbow.
• SNAPs are normal in radiculopathy.
• Median neuropathy would show changes in median nerve SNAPs and CMAPs (digits 1-4, not 5).
Which of the following involves the postsynaptic portion of the neuromuscular junction?
A Myasthenia Gravis (MG)
B Post-Polio Syndrome
C Botulism
D Lambert-Eaton Syndrome (LEMS)
Answer: A
Explanation:
• Lambert-Eaton Syndrome (LEMS) and Botulism are presynaptic neuromuscular junction (NMJ) disorders.
• Post-Polio Syndrome involves the burning out and subsequent death of anterior horn cells that survived a patient’s remote history of polio.
• Myasthenia Gravis (MG) is truly a postsynaptic NMJ disease involving antibodies against the acetylcholine receptor on the postsynaptic membrane.
During an exam, perhaps much like this one, when a question stem mentions EMG findings of painless myokymia in C5-C6/upper trunk muscles, you will astutely recall that the most likely etiology of these findings is which of the following?
A Radiation plexopathy
B Active denervation
C Myotonia congenita
D Pancoast tumor
Answer: A
Explanation:
• Radiation plexopathy is classically the cause of myokymia found on EMG, which classically affects C5-C6/upper trunk muscles, and is usually a painless finding.
• Lower trunk plexopathy with pain is concerning for pancoast (lung) tumor compressing the lower trunk of the brachial plexus.
• Myotonia congenita will demonstrate myotonic discharges (divebomber sound).
• Active denervation will demonstrate fibrillations and positive sharp waves.
• Examiners thoroughly enjoy asking you about radiation plexopathy and myokymia, so be sure to know this topic well.
A 71 year-old male survives sepsis due to pneumonia. You are consulted to perform an inpatient EMG due to severe weakness reported. The patient complains of weakness in both upper and lower limbs. He denies numbness, tingling, or bowel/bladder dysfunction. NCS reveals normal sensory nerve action potentials (SNAPs) of median, ulnar, radial, superficial fibular, and sural nerves on the left side of the body. There is decreased amplitude of median, ulnar, tibial, and fibular nerve compound muscle action potentials (CMAPs). EMG reveals increased recruitment of abductor pollicis brevis, first dorsal interosseous, deltoid, rectus femoris, gastrocnemius, and tibialis anterior. Which of the following is the most likely diagnosis?
A Steroid myopathy
B Guillain-Barre syndrome
C Critical illness neuropathy
D Critical illness myopathy
Answer: D
Explanation:
• Critical illness myopathy (CIM) presents classically as proximal and distal weakness in a critical illness setting (e.g. sepsis/SIRS) with normal sensation and normal SNAPs, and short-duration, small amplitude, early recruitment motor units on EMG - a classic myopathic EMG pattern
○ SNAPs are normal in CIM, as the nerves are not affected.
• Critical illness neuropathy will show SNAP abnormalities and a “neuropathic” recruitment pattern (decreased recruitment).
• Guillain-Barre syndrome typically presents with sensory abnormalities, gradual onset weakness, and recent history of GI infection or upper respiratory tract infection.
○ There is also increased temporal dispersion and conduction block in Guillain-Barre syndrome.
• Steroid myopathy is due to corticosteroid usage, and typically demonstrates a normal EMG, as it affects type 2 muscle fibers (EMG essentially only examines type 1 muscle fibers).
The first sign of Guillain Barre Syndrome on electrodiagnostic studies is which of the following?
A Prolonged M wave
B Prolonged A wave
C Prolonged F wave
D Prolonged H reflex
Answer: C
Explanation:
• Prolonged or absent F waves are the first sign of GBS on EDX studies.
The medial antebrachial cutaneous nerve (MAC) arises in which of the following ways?
A None of these answers is correct
B As a direct branch of the ulnar nerve
C As the continuation of the lower trunk of the brachial plexus
D As a direct branch of the medial cord of the brachial plexus
Answer: D
Explanation:
• The medial antebrachial cutaneous (MAC) nerve arises as a branch of the medial cord of the brachial plexus.
Which of the following EMG/NCS findings is associated with post-polio syndrome? MUAP: motor unit action potential. SNAP: sensory nerve action potential. CMAP: compound muscle action potential.
A Large amplitude CMAPs
B Giant MUAPs
C Absent SNAPs
D >10% CMAP amplitude decrement during repetitive nerve stimulation
Answer: B
Explanation:
• Post-polio syndrome (“burning out” and death of anterior horn cells in a patient with a history of polio who recovered decades ago) is associated with giant MUAPs on EMG.
• This is essentially because a few anterior horn cells are doing all the work of the contracting the muscles, and so there are very few MUAPs to study, as all the muscle fibers belong to just a few anterior horn cells.
• SNAPs are unaffected in anterior horn cell disease.
• CMAP amplitudes are low in post-polio syndrome.
• CMAP decrement during repetitive nerve stimulation is indicative of neuromuscular junction disease, NOT post-polio syndrome.
Which of the following genetic sequences is associated with Charcot-Marie-Tooth (CMT) Neuropathy type Ia?
A Duplication of SMN-1
B Deletion of SMN-1
C Duplication of PMP-22
D Deletion of PMP-22
Answer: C
Explanation:
• Charcot-Marie-Tooth Neuropathy type Ia (CMT1A) is associated with duplication of the PMP-22 gene.
• Hereditary neuropathy with liability to pressure palsy (HNPP) is associated with deletion of PMP-22.
• Mutations of the SMN-1 gene are the cause of spinal muscular atrophy and its subtypes.
Motor nerve conduction studies are typically recorded in which way?
A Counterdromically
B Prodromically
C Orthodromically
D Antidromically
Answer: C
Explanation:
• Motor NCS are recorded orthodromically; the nerve is shocked, and the action potential travels distally down the axon just like it does in everyday life.
• Sensory nerve studies are typically recorded antidromically.
Which of the following muscles is NOT innervated by the posterior interosseous nerve?
A Extensor digitorum
B Extensor carpi radialis longus
C Extensor indicis proprius
D Extensor carpi ulnaris
Answer: B
Explanation:
• The ECRL is innervated by the radial nerve, not the posterior interosseous nerve (which arises from the radial nerve).
A 25 year-old male develops 2 days of progressive lower limb weakness. He has a history of recent gastroenteritis. Bilateral lower limb EMG/NCS reveals prolonged latency of bilateral superficial fibular nerve SNAPs (sensory nerve action potentials), but normal sural nerve SNAPs. The bilateral CMAPs to the EDB and AH (compound muscle action potentials to the extensor digitorum brevis and abductor hallucis) show prolonged latency but normal amplitude. EMG reveals decreased recruitment in the bilateral EDB, AH, tibialis anterior, gastrocnemius, and semimembranosus, but normal activity in rectus femoris and adductor longus. Which of the following additional EMG/NCS findings would most likely be discovered in this patient?
A Any of the above depending on severity
B Decreased temporal dispersion
C Normal temporal dispersion
D Increased temporal dispersion
Answer: D
Explanation:
• This patient presents with Guillain-Barre Syndrome (GBS), also referred to as AIDP (acute inflammatory demyelinating polyradiculopathy).
• GBS is caused by a recent infection (typically GI or URI) causing your immune system to confuse a foreign protein with a protein on your own myelin. Thus, your body destroys your own peripheral nerve myelin (demyelinating the nerves and prolonging the latency).
• The first EMG finding of GBS is delayed or absent F-waves.
• NCS reveals prolonged latency and sometimes reduced amplitude of SNAPs with sural nerve sparing, as the sural nerve is larger with more myelin than other peripheral sensory nerves, and thus is less affected than the other nerves.
• CMAPs show prolonged latency, decreased conduction velocity (CV), and typically normal amplitude (this is a demyelinating disease primarily, NOT axonal loss). =
• EMG shows decreased recruitment but otherwise there should be NO active denervation usually, but this can occur as a secondary feature of GBS weeks after onset.
• Abnormal/increased temporal dispersion is also a feature of this disease on NCS, due to the widespread and more uniform demyelination of nerves taking place.
• Treatment involves PT and early plasmapheresis/IVIG.
Which of the following muscles is most likely to develop weakness following a proximal humerus surgical neck fracture?
A Extensor carpi radialis brevis (ECRB)
B Infraspinatus
C Teres minor
D Supraspinatus
Answer: A
Explanation:
• The axillary nerve is at greatest risk of injury following a surgical neck fracture.
• The only muscle listed that is innervated by the axillary nerve is teres minor.
• Deltoid (not listed) would have also been an acceptable answer.
• Supraspinatus and infraspinatus are innervated by the suprascapular nerve.
• ECRB is innervated by the radial nerve.
Which of the following muscles is innervated by the lateral cord of the brachial plexus?
A Flexor digitorum profundus to digits 2,3
B Brachioradialis
C Flexor carpi radialis
D Deltoid
Answer: C
Explanation:
• The deltoid and brachioradialis are innervated by the posterior cord.
• The flexor digitorum profundus 2,3 is innervated by the medial cord.
• The flexor carpi radialis is innervated by the lateral cord.
Demyelination will most likely result in which of the following nerve conduction study (NCS) results?
A Increased amplitude, prolonged latency, decreased temporal dispersion
B Normal amplitude, prolonged latency, decreased temporal dispersion
C Normal amplitude, prolonged latency, increased temporal dispersion
D Decreased amplitude, prolonged latency, increased temporal dispersion
Answer: C
Explanation:
• Demyelination is the stripping of the myelin sheath around axons. As myelin increases conduction velocity of axons (decreasing their latency), removal of this myelin will cause slowed conduction velocity, prolonged latency (it takes a longer time for the action potential to reach the recording electrode), and increased temporal dispersion.
• Temporal dispersion is the widening of the SNAP or CMAP due to impulses reaching the recording electrode at widely varying times (due to demyelination decreasing the uniformity of signal transmission along a nerve’s axons).
• Amplitude decrease occurs with axonal loss. Amplitude increase occurs in cold limbs.
During an EMG, a patient is found to have active denervation of the pronator teres and abductor pollicis brevis. Which of the following statements is most likely to be true?
A The patient will demonstrate thumb flexion weakness
B The patient will demonstrate distal interphalangeal joint flexion weakness to digits 4 and 5
C The patient will demonstrate wrist flexion with medial deviation weakness
D The patient will demonstrate wrist extension weakness
Answer: A
Explanation:
• This patient has median neuropathy at the elbow.
• Thus, flexor pollicis longus (FPL) will be affected and potentially weak, making “thumb flexion weakness.”
• Wrist flexion with medial deviation weakness, and DIP flexion weakness to digits 4 and 5 represent ulnar nerve muscle functions (flexor carpi ulnaris and flexor digitorum profundus to digits 4 and 5), and wrist extension weakness represents a radial nerve muscle function.
• Remember that medial deviation of the wrist = ulnar deviation with respect to conventional anatomic position.
During nerve conduction studies, why do we refer to the CMAP as the “compound” muscle action potential?
A Because the CMAP is recorded orthodromically, firing a greater number of axons than antidromically
B Because CMAP records activity from multiple muscles in the vicinity of the recording electrode
C Because the CMAP records input from multiple nerve branches
D Because the CMAP records an electrical summation of all muscle fibers of a single muscle contraction
Answer: D
Explanation:
• The CMAP, though it is only one nerve and one muscle that are being intentionally stimulated, is the recording of all the many muscle fibers that this nerve, being stimulated, has caused to depolarize and contract.
• Sometimes the CMAP does record activity from other muscles near the recording electrode, but this is never the intention, and typically corrections are attempted to avoid other muscle signals.
A patient’s left upper limb EMG/NCS results are as follows. Routine median, ulnar, and radial sensory nerve conduction studies are normal. The lateral antebrachial cutaneous nerve SNAP (sensory nerve action potential) shows decreased amplitude when compared to the contralateral side. EMG reveals decreased recruitment and 1+ positive sharp waves in biceps and brachialis, but normal deltoid, triceps, brachioradialis, extensor indicis proprius, flexor digitorum profundus, abductor pollicis brevis, and first dorsal interosseous. Which of the following muscles would also be expected to demonstrate EMG abnormalities in this patient?
A Infraspinatus
B Teres minor
C Anconeus
D Pronator teres
Answer: B
Explanation:
• Lateral cord brachial plexopathy: affects biceps, brachialis, coracobrachialis, pronator teres, flexor carpi radialis, flexor digitorum superficialis, pronator quadratus, flexor pollicis longus, pectoralis major, and lateral antebrachial cutaneous nerve.
• Thus, pronator teres is the best answer.
During nerve conduction studies, the optimal lower limb temperature is which of the following?
A 33 degrees Celsius
B 32 degrees Celsius
C 31 degrees Celsius
D 30 degrees Celsius
Answer: D
Explanation:
• The optimal lower limb temperature during NCS is 30 degrees Celsius.
• The optimal skin temperature for NCS should be at least 32 ° C for upper extremities and 30 ° C for lower extremities.
• As skin temperature drops, the CMAP amplitude increases and the CMAP latency and velocity prolong.
During an EMG study, needling of the flexor pollicis longus and pronator quadratus reveal 2+ fibrillations and positive sharp waves, while the remaining muscles (abductor pollicis brevis, first dorsal interosseous, flexor carpi radialis, biceps brachii, triceps, cervical paraspinals) are normal. Which of the following is the most likely diagnosis?
A Anterior interosseous neuropathy
B Medial cord brachial plexopathy
C Median neuropathy at the elbow
D Posterior interosseous neuropathy
Answer: A
Explanation:
• The flexor pollicis longus, pronator quadratus, and flexor digitorum profundus to digits 2,3 are all innervated by the anterior interosseous nerve (AIN).
• Posterior interosseous neuropathy (PIN-opathy) would show abnormal EMG to PIN-innervated muscles (extensor digitorum, extensor indicis proprius, extensor carpi ulnaris, extensor pollicis longus).
• Median neuropathy at the elbow would show abnormalities in median nerve muscles (flexor carpi radialis, for example) in addition to some AIN muscles.
• Medial cord-opathy would show changes in other medial cord muscles, such as the first dorsal interosseous, which was normal in this study.
Which of the following muscles receives its innervation via the following neural pathway? C7, C8, T1; middle and lower trunk; medial and lateral cord; median nerve; anterior interosseous nerve.
A Lumbricals 1 and 2
B Flexor carpi radialis
C Flexor digitorum superficialis
D Pronator quadratus
Answer: D
Explanation:
• Pronator quadratus is innervated by the above pathway.
• FDS, FCR, and lumbricals 1 and 2 are all directly innervated by the median nerve, NOOT the anterior interosseous nerve.
An axon is regrowing down a nerve. Finally, after many months of searching, it has returned to its original muscle fibers that it used to innervate. However, to its dismay, it discovers that another axon has sprouted collateral branches which are currently supplying our hero axon’s former muscle fibers. The two axons decide to compete for muscle fiber dominance. Which axon will ultimately prevail and maintain control of these muscle fibers?
A Whichever axon possesses the largest size with the strongest neuromuscular junction connections
B Whichever axon has a larger predominance of Type I fibers
C The current axon innervating the muscle fibers
D The original axon innervating the muscle fibers
Answer: A
Explanation:
• The biggest motor neuron with the strongest NMJ connection will “win” control of a given muscle fiber.
Some individuals possess a normal anatomic variant by which their median nerve motor fibers in the hand cross over to join the ulnar nerve. Which of the following is the correct name for this variant?
A Shelley-Webster anastomosis
B Martin-Gruber anastomosis
C Kertley-Thompson anastomosis
D Riche-Cannieu anastomosis
Answer: D
Explanation:
• Riche-Cannieu anastomosis involves median motor fibers in the hand crossing over to join the ulnar nerve; classically this can cause the ulnar nerve to supply motor control to the entire hand.
• Martin-Gruber anastomosis is another anatomic variant involving median nerve fibers crossing over in the forearm to innervate the ulnar nerve and supply some ulnar nerve muscles in the hand.
• “Kertley-Thompson anastomosis” and “Shelley-Webster anastomosis” are fictional. Perhaps Kertley and Thompson are indeed out there, searching for their anastomosis of fame.
Lowering the high frequency filter during NCS will cause which of the following changes?
A Shortened peak latency, shortened onset latency
B Shortened peak latency, prolonged onset latency
C Prolonged peak latency, shortened onset latency
D Prolonged peak latency, prolonged onset latency
Answer: D
Explanation:
• Lowering the high frequency filter during NCS will cause prolonged peak and onset latencies.
What is the primary rationale for not applying cold over an area of skin that has poor blood supply due to peripheral vascular disease (PVD)?
A Cold is actually not contraindicated over areas having poor blood supply
B It may worsen pain
C Cold decreases blood flow to its area of application
D It may facilitate cellulitis
Answer: C
Explanation:
• Cold’s effect is to decrease metabolism locally, and decrease blood flow to an area of skin.
• In cases of skin breakdown, insensate skin, and PVD, this may cause worsened skin breakdown or worsened tissue ischemia (specifically in PVD).
Which of the following is the main problem with performing the Phalen test with the elbows flexed instead of extended?
A None of these answers is correct
B A positive test is less informative
C Traction is applied to the middle cervical roots
D The median nerve is not stressed enough
Answer: B
Explanation:
• When performing the Phalen test (flexing the wrists, holding this posture, and eliciting hand numbness/tingling due to median nerve compression within the carpal tunnel), it is best performed with the patient’s elbows extended.
• Flexing the elbows stretches the ulnar nerve and may irritate an already irritated ulnar nerve, thus causing hand numbness and tingling NOT due to median nerve compression.
• Thus, a positive test in that case would NOT allow you to narrow it down between ulnar neuropathy and median neuropathy - it is less informative.
During a nerve conduction study, you decide to place the recording electrode over the patient’s soleus, and the reference electrode over their achilles tendon. You then stimulate in a proximal direction from the popliteal fossa. When you examine the waveform produced by this, you note prolonged latency. What is the most appropriate conclusion from these results?
A There is damage somewhere along the pathway you stimulated
B There is uniform, but not focal, demyelination
C There is axonal loss
D There is a conduction block
Answer: A
Explanation:
• The acquisition of the H reflex is described here. By performing this, the physician stimulates the Ia sensory afferent nerves and records over the muscle (soleus), sending the action potential proximally toward the spinal cord, triggering the spinal reflex arc, and sending the action potential back down distally along the motor nerve (sciatic → tibial) to make the muscle (soleus) contract.
• Prolonged latency of this clearly very long nerve pathway merely indicates that there is some kind of damage somewhere along the pathway that has caused the signal to take much longer to reach the recording electrode than is normal.
• The H reflex study is typically used to assess for S1 radiculopathy.
A 42 year-old male presents for a left upper limb EMG/NCS. During the study you detect prolonged latency of the sensory nerve action potential (SNAP) to the anatomic snuffbox, with normal SNAPs to digits 2 and 5. Needle EMG reveals decreased recruitment and 2+ fibrillations in brachioradialis and extensor indicis proprius (EIP), with normal EMG of deltoid, biceps brachii, triceps, pronator teres, first dorsal interosseous, and abductor pollicis brevis. Which of the following is the most likely cause of the patient’s symptoms?
A Compression by the ligament of Struthers
B Midshaft humerus fracture
C Compression by the Arcade of Frohse
D Improper crutch use
Answer: B
Explanation:
• This patient presents with EMG/NCS findings localizing to the radial nerve at or just proximal to the elbow.
• Midshaft humerus fractures classically produce radial neuropathy that spares the triceps and anconeus (as these muscles are innervated prior to the humeral midshaft area - the spiral groove).
• Improper crutch use can cause a proximal radial neuropathy, but that would demonstrate EMG abnormalities in the triceps/anconeus, and the triceps is normal in this patient’s study.
• Compression by the Arcade of Frohse can cause posterior interosseous neuropathy (PIN-opathy) - a pure motor neuropathy that would spare brachioradialis (not a PIN-innervated muscle) and show normal radial SNAPs (our radial SNAP in this patient’s study is abnormal).
• Ligament of Struthers can cause median neuropathy at the elbow, and our median nerve studies are normal in this patient.
A patient’s right upper limb EMG/NCS results are as follows. Routine median, ulnar, and radial sensory nerve conduction studies are normal. EMG reveals decreased recruitment and 3+ fibrillations in supraspinatus, deltoid, biceps, and brachioradialis. EMG of triceps, pronator teres, extensor indicis proprius, abductor pollicis brevis, and first dorsal interosseous is normal. Which of the following is the most likely diagnosis?
A Lateral cord brachial plexopathy
B Upper trunk brachial plexopathy
C C6 radiculopathy
D C5 radiculopathy
Answer: D
Explanation:
• C5 radiculopathy is the best answer.
• All upper limb muscles receiving C5 innervation are affected (infraspinatus, brachialis, and teres minor are untested, but could be expected to show changes as well).
• Muscles with C5-C6 innervation are affected (supraspinatus, deltoid, biceps, and brachioradialis), but those without any C5 innervation are spared (all remaining muscles).
• Pronator teres has C6-C7 innervation, thus it is spared.
• Upper trunk plexopathy would be expected to show median sensory abnormalities on NCS, as well as pronator teres and possibly triceps being affected.
• Lateral cord plexopathy would affect biceps, brachialis, coracobrachialis, pronator teres, flexor carpi radialis, flexor digitorum superficialis, pronator quadratus, flexor pollicis longus, pectoralis major, and lateral antebrachial cutaneous nerve.
• Remember, sensory nerve action potentials are always normal in a purely radiculopathic process.
During EMG studies, decreased insertional activity can be seen in which of the following situations?
A None of these answers is correct
B Normal
C Muscle fibrosis
D Active denervation
Answer: C
Explanation:
• Muscle fibrosis can cause decreased insertional activity.
• Increased insertional activity can be seen in cases in which the muscle cell membrane is hyper-irritable, such as active denervation.
A stretch injury to a nerve that leads to axon loss with intact epineurium is also known as which of the following?
A Conduction block
B Neurapraxia
C Axonotmesis
D Neurotmesis
Answer: C
Explanation:
• This question describes axonotmesis. Even though the axons have died due to crush/stretch injury, the epineurium is still intact, which will serve as a guide path for the axons to regenerate along and ultimately find their target muscle fibers again.
The subscapularis differs from the rest of the rotator cuff muscles in what way?
A None of these answers is correct
B It is the only muscle innervated by the posterior cord of the brachial plexus
C It is the only muscle to insert onto the greater tuberosity of the humerus
D It is the only internal rotator of the rotator cuff
Answer: D
Explanation:
• Subscapularis performs internal rotation of the shoulder.
• Supraspinatus performs abduction.
• Infraspinatus and Teres minor perform external rotation.
• Subscapularis inserts onto the lesser tuberosity of the humerus.
• Teres minor also shares innervation from the posterior cord of the brachial plexus.
A patient’s right upper limb EMG/NCS results are as follows. Routine median, ulnar, and radial sensory nerve conduction studies are normal except for prolonged latency of median SNAP to digit 2 and ulnar SNAP to digit 5. EMG reveals decreased recruitment and polyphasic potentials in triceps, extensor indicis proprius, flexor digitorum profundus to digits 2-5, flexor carpi ulnaris, abductor pollicis brevis, and abductor digiti minimi, but normal activity in supraspinatus, deltoid, biceps, brachioradialis, and flexor carpi radialis. Which of the following is the most likely diagnosis?
A Lower trunk brachial plexopathy
B Middle trunk brachial plexopathy
C C8 radiculopathy
D C7 radiculopathy
Answer: A
Explanation:
• This is a lower trunk plexopathy.
• Radiculopathy would spare the SNAPs, which are affected here for both the median and ulnar nerves.
• Middle trunk plexopathy would affect the flexor carpi radialis, which is spared here.
A 29 year-old female presents to your clinic with complaints of 2 months of bilateral hand numbness and tingling, worse at night. She is expecting her first child later this year. On exam, strength and sensation are intact. What is the next best step?
A Physical therapy
B EMG
C MRI cervical spine
D Bracing
Answer: D
Explanation:
• Carpal tunnel syndrome is typically worse at night and wakes patients up while they sleep (or worse upon waking up in the morning).
• Pregnancy can cause carpal tunnel syndrome, simply due to fluid balance changes in the body.
• The first step is a carpal tunnel wrist brace that is to be worn during sleep, which prevents wrist flexion (wrist flexion causes increased pressure within the carpal tunnel, compressing and irritating the median nerve over time).
• NSAIDs may be trialed if NOT currently pregnant.
• If this fails, EMG should be considered to determine the cause and severity of the problem.
• If carpal tunnel syndrome is confirmed (median neuropathy at the wrist), carpal tunnel injection vs. surgical release should be considered, depending on severity.
• MRI of the cervical spine would NOT be indicated unless myelopathy were suspected (hyperreflexia, weakness, sensory abnormalities), or radiculopathy that fails conservative treatments (PT, epidural injections) or is progressively worsening.
• Occupational therapy can help but does have somewhat limited value in carpal tunnel syndrome. Physical therapy would be less appropriate vs. occupational therapy for CTS.
A patient’s left upper limb EMG/NCS results are as follows. Routine median, ulnar, and radial sensory nerve conduction studies are normal, except for decreased amplitude of the sensory nerve action potential (SNAP) to the anatomic snuffbox. EMG reveals decreased recruitment and 1+ fibrillations in deltoid, brachioradialis, and triceps, but normal EMG in biceps, pronator teres, flexor pollicis longus, abductor pollicis brevis, and first dorsal interosseous. Which of the following muscles would also be expected to exhibit EMG abnormalities in this patient?
A Pectoralis major
B Pronator quadratus
C Extensor indicis proprius
D Infraspinatus
Answer: C
Explanation:
• Posterior cord plexopathy, as evidenced by all posterior cord-innervated muscles being affected, and all non-posterior-cord muscles being spared, in addition to the radial nerve SNAP (snuffbox) being abnormal.
• Of the answer choices, only extensor indicis propius (EIP) is a posterior cord muscle; thus, EIP is correct.
During a patient examination for left shoulder pain you notice that the patient’s left scapula sits more medially than the right scapula. The nerve implicated in this patient’s condition receives its innervation from which trunk of the brachial plexus?
A None of these answers is correct
B Lower
C Middle
D Upper
Answer: A
Explanation:
• Long thoracic nerve innervates the serratus anterior.
• Injury to the long thoracic nerve can cause a medially winged scapula, as this patient demonstrates.
• The serratus anterior innervation is C5, C6, C7, long thoracic nerve.
• Thus, its innervation is pre-plexus, and does NOT have any trunks or cords that contribute to it.
A previously healthy 53 year-old female presents with gradual onset weakness, worse with any type of exercise, climbing stairs, and worse as the day progresses. She does not smoke, drink alcohol, or use illicit drugs. She notices associated double vision at times, worse as the day progresses. She denies trauma or bowel/bladder abnormalities. Which of the following etiologies is most likely responsible for her symptoms?
A “Burning out” of already sparse anterior horn cells
B Presence of antibodies against postsynaptic acetylcholine receptors
C Presence of antibodies against presynaptic calcium channels
D Malignant growth of cells
Answer: B
Explanation:
• Myasthenia gravis (MG) is due to antibodies against postsynaptic neuromuscular junction (NMJ) acetylcholine receptors.
○ Classically symptoms (proximal muscle weakness) worsen with exercise, as the day progresses, and are associated with diplopia.
• Lambert-Eaton Myasthenic Syndrome (LEMS) is due to antibodies against presynaptic calcium channels, and presents with proximal muscle weakness that improves with exercise.
○ LEMS is also commonly secondary to a paraneoplastic process brought on by small cell lung carcinoma (malignant growth of cells).
• Post-polio syndrome : the burning out of sparse anterior horn cells in patients who present with weakness decades after surviving polio and recovering.
Once a patient has reached age 50, the conduction velocity of their nerves will decrease by approximately how many meters per second for each subsequent decade?
A 15
B 8
C 4
D 2
Answer: D
Explanation:
• After age 50, conduction velocity normally decreases by about 2 m/s per decade.
You are performing an EMG/NCS on a patient. The sensory nerve action potential (SNAP) to digit 2 and compound motor action potential (CMAP) to the abductor pollicis brevis are normal. The SNAP to digit 5 reveals prolonged latency. The CMAP to the abductor digiti minimi is normal. Needle EMG reveals no abnormalities. Which of the following is the most likely diagnosis?
A Medial cord plexopathy
B Severe ulnar neuropathy
C Mild ulnar neuropathy
D Normal study
Answer: C
Explanation:
• Mild ulnar neuropathy is most consistent with an otherwise normal study with isolated prolonged ulnar SNAP - indicating ulnar nerve changes somewhere, most likely between and including the elbow and the wrist.
• All values would have to be normal for this to be recorded as a normal study.
• Medial cordopathy would have to be better supported, possibly including an abnormal medial antebrachial cutaneous SNAP.
• Finally, severe ulnar neuropathy would show active denervation in ulnar nerve muscles, not shown here.
The suprascapular nerve innervates the supraspinatus. It then passes through which structure on its way to innervate the infraspinatus?
A Scapulothoracic notch
B Spinoglenoid notch
C Dorsal scapular notch
D Suprascapular notch
Answer: B
Explanation:
• Suprascapular nerve passes through the spinoglenoid notch to innervate the infraspinatus.
During nerve conduction studies, the act of stimulating a motor nerve in a proximal (antidromic) direction and recording from a distal muscle innervated by this nerve is performed in order to obtain which of the following signals?
A M wave
B F wave
C A wave
D H reflex
Answer: B
Explanation:
• This question describes how to obtain an F wave.
• For example, recording over the first dorsal interosseus muscle and antidromically stimulating the ulnar nerve at the wrist will send an action potential antidromically back up, all the way to the anterior horn, which will then depolarize a random population of anterior horn cells, whose own depolarization will then travel back down the axons of the ulnar nerve and will be recorded by the recording electrode over the first dorsal interosseus muscle.
• Thus, this signal, the F wave, is NOT actually a true reflex, although it is sometimes called the “F reflex”.
A 54 year-old male presents with right lateral thigh burning pain with numbness and tingling for the past 3 months. On exam, he is able to trace an ovoid patch on his anterolateral thigh where the abnormal sensations exist. Strength and reflexes are intact. He denies bowel or bladder dysfunction. Which of the following historical findings is most likely present on further questioning?
A History of hypertension
B History of hip joint avascular necrosis (AVN)
C Wearing tight belts
D History of lumbar spine surgery
Answer: C
Explanation:
• Lateral femoral cutaneous neuropathy (LFCN-opathy, meralgia paresthetica)
• Eentrapment/compression of this nerve typically as it passes underneath the inguinal ligament.
• It innervates an ovoid patch of skin on the anterolateral thigh, but does NOT innervate muscles. Thus there will be NO muscle weakness, and routine EMG/NCS will be normal.
• LFCN SNAP will be abnormal, and this should be compared to the unaffected side.
• LFCN-opathy is associated with diabetes, wearing tight belts/underwear, obesity, and rapid weight changes.
• It is usually self-limiting but can be treated with physical therapy, neuropathic pain medication (e.g. gabapentin), LFCN block or hydrodissection with ultrasound guidance, or surgical decompression and release.
When needling a patient’s biceps brachii during an EMG study, you detect an involuntary, abrupt, regular signal that sounds like soldiers marching. What is the most likely diagnosis?
A Normal
B Amyotrophic lateral sclerosis (ALS)
C Pancoast tumor
D Radiation plexopathy
Answer: D
Explanation:
• Myokymia, as described here, is classically seen in upper trunk radiation plexopathy.
• Pancoast lung tumors would typically cause a painful lower trunk plexopathy.
• ALS is NOT usually included in discussions of myokymia.
Complex repetitive discharges occur via which of the following mechanisms?
A Myopathy
B Potassium depletion
C Ephaptic transmission
D Active denervation
Answer: C
Explanation:
• Complex repetitive discharges (CRD) is an involuntary discharge that is very wide and serrated (complex in appearance, and repetitive in firing) and occurs due to a motor unit being denervated and then reinnervated by another motor neuron, which itself then becomes denervated.
• Ephaptic transmission is the process by which these muscle fibers all fire regularly together.
Complex repetitive discharges are seen in chronic radiculopathy, anterior horn cell disease, and some normal patients.
A 30 year-old male is involved in a motorcycle collision and develops sudden-onset severe right arm pain. He has bruising and swelling of his upper arm on exam. Xrays reveal a mid-shaft humeral fracture. Which of the following muscles is most important to test for strength?
A All of the listed choices are equally useful
B Anconeus
C Triceps
D Extensor carpi radialis brevis (ECRB)
Answer: D
Explanation:
• Midshaft humeral fractures commonly cause radial neuropathy due to the close proximity of the radial nerve to the humerus at this location.
• At the level of the midshaft of the humerus, the triceps and anconeus are already innervated.
• Thus, you must examine downstream radial nerve muscles to assess integrity of the radial nerve. In this case, extensor capi radialis brevis (ECRB) is the only muscle listed that has yet to be innervated by the radial nerve. Thus, it should be affected if the radial nerve has been damaged by this fracture.
• A positive exam would yield impaired strength in wrist extension.
You are assessing a patient for an L5 radiculopathy. As a sharp physiatrist, you decide to test the strength of the extensor hallucis longus (EHL), which is 4/5. Which of the following functions would be most useful to test next?
A Ankle inversion
B Thigh adduction
C Plantarflexion
D Knee extension
Answer: A
Explanation:
• The only function here which is performed by an L5-innervated muscle is ankle inversion (tibialis posterior - L5, S1; sciatic nerve; tibial nerve).
• Knee extension is performed by the quadriceps (L2, L3, L4).
• Plantarflexion is controlled by the gastrocnemius-soleus complex (S1, S2; sciatic nerve; tibial nerve).
• Thigh adduction is controlled by the adductor muscles (L2, L3, L4; obturator nerve).
Which of the following innervation pathways belongs to the extensor digitorum brevis (EDB)?
A L5, S1; sciatic nerve; deep fibular nerve
B L4, L5, S1; sciatic nerve; tibial nerve
C L4, L5; sciatic nerve; deep fibular nerve
D L4, L5, S1; sciatic nerve; deep fibular nerve
Answer: D
Explanation:
• “L4, L5, S1; sciatic nerve; deep fibular nerve” is the correct innervation for extensor digitorum brevis (EDB), as well as extensor hallucis longus (EHL).
Which of the following is the correct innervation pathway for the flexor digitorum profundus to digits 2 and 3?
A C8, T1; lower trunk; medial cord; median nerve
B C8, T1; middle and lower trunk; medial and lateral cord; median nerve; anterior interosseous nerve
C C7, C8, T1; middle and lower trunk; medial cord; median nerve; anterior interosseous nerve
D C7, C8, T1; middle and lower trunk; medial cord; median nerve
Answer: C
Explanation:
• The flxor digitorum profundus (FDP) 2,3 is innervated via the pathway: C7, C8, T1; middle and lower trunk; medial cord; median nerve; anterior interosseous nerve
Which of the following muscles does not share L4 root innervation?
A Gluteus maximus
B Gluteus medius
C Tibialis anterior
D Iliopsoas
Answer: A
Explanation: • Iliopsoas: L2, L3, L4. • Tibialis anterior: L4, L5. • Gluteus medius: L4, L5, S1. • Gluteus maximus: L5, S1, S2.
A 48 year-old male develops right thigh pain and weakness. Strength testing of hip flexion, knee extension, dorsiflexion, great toe extension, and plantarflexion is normal. EMG/NCS reveals normal sensory nerve action potentials (SNAPs) of sural and superficial fibular nerves, and normal compound muscle action potentials (CMAPs) to the extensor digitorum brevis and abductor hallucis. Needle EMG reveals decreased recruitment and 2+ fibrillations in adductor longus, and normal activity in abductor hallucis, extensor digitorum brevis, gastrocnemius, rectus femoris, tensor fascia lata, and lumbar paraspinals. Which of the following is the most likely diagnosis?
A L4 radiculopathy
B Obturator neuropathy
C L3 radiculopathy
D Femoral neuropathy
Answer: B
Explanation:
• Obturator neuropathy typically due to trauma such as a pelvic fracture
• Femoral neuropathy and L3/L4 radiculopathy would show abnormal activity in the quadriceps, which are spared in this patient.
• This patient would also demonstrate thigh adduction weakness, which was NOT evaluated in this patient.
A 56 year-old male with a history of cancer within the posterior triangle of the neck presents to you with 5 months of left shoulder pain. On exam, his left scapula rests more laterally than his right scapula. This problem is most likely the result of injury to which of the following nerves?
A Thoracodorsal
B Long thoracic
C Spinal accessory
D Dorsal scapular
Answer: C
Explanation:
• Laterally winged scapula indicates upper/middle trapezius muscle weakness, which is most commonly due to spinal accessory neuropathy.
• The spinal accessory nerve passes through the posterior triangle of the neck and can be impinged by structures or abnormal masses in this area.
• Long thoracic nerve innervates the serratus anterior, and injury to this nerve can cause a medially winged scapula (not laterally winged).
• Injury to the thoracodorsal nerve, which innervates the latissimus dorsi, does NOT cause a winged scapula.
• Injury to the dorsal scapular nerve (which innervates the rhomboids) is rare, and would potentially also be a cause of laterally winged scapula. However, the most likely answer remains the spinal accessory nerve.
Which of the following muscles is NOT innervated by the sciatic nerve (tibial division)?
A Short head of biceps femoris
B Semitendinosus
C Long head of biceps femoris
D Semimembranosus
Answer: A
Explanation:
• Semimembranosus, semitendinosus, and the long head of biceps femoris are all innervated by the sciatic nerve (tibial division).
• The short head of the biceps femoris is innervated by the sciatic nerve (common fibular division).
Neurogenic thoracic outlet syndrome can be most accurately described as which of the following statements?
A None of these answers is correct
B Middle trunk brachial plexopathy
C Lower trunk brachial plexopathy
D Upper trunk brachial plexopathy
Answer: C
Explanation:
• Neurogenic thoracic outlet syndrome is essentially a lower trunk brachial plexopathy (involving C8, T1 nerve roots).
Which of the following EMG/NCS findings would indicate nerve compression by the Arcade of Frohse? SNAP: sensory nerve action potential. BR: brachioradialis. EIP: extensor indicis proprius.
A Normal SNAPs to digits 1,2,5, snuffbox. Abnormal EMG to BR and EIP
B Normal SNAPs to digits 1,2,5, abnormal snuffbox SNAP. Normal EMG to BR. Abnormal EMG to EIP
C Normal SNAPs to digits 1,2,5, snuffbox. Normal EMG to BR. Abnormal EMG to EIP
D Normal SNAPs to digits 1,2,5; abnormal snuffbox SNAP. Abnormal EMG to BR and EIP
Answer: C
Explanation:
• Compression by the Arcade of Frohse can cause posterior interosseous neuropathy (PIN-opathy) - a pure motor neuropathy that would spare brachioradialis (not a PIN-innervated muscle) and show normal radial SNAPs.
• Choice “Normal SNAPs to digits 1,2,5, snuffbox. Abnormal EMG to BR and EIP” shows abnormal BR EMG, which would be spared in a PIN-opathy.
During an EMG/NCS study, routine sensory nerve action potentials (SNAPs) and compound muscle action potentials (CMAPs) are normal. Needle EMG reveals abnormal spontaneous activity in the infraspinatus, and normal EMG of the cervical paraspinals, deltoid, supraspinatus, triceps, pronator teres, abductor pollicis brevis, and first dorsal interosseous. Which of the following is the most likely diagnosis?
A C5 radiculopathy
B Suprascapular neuropathy distal to the spinoglenoid notch
C Suprascapular neuropathy proximal to the spinoglenoid notch
D Upper trunk brachial plexopathy
Answer: B
Explanation:
• Suprascapular nerve innervates the supraspinatus, then passes through the spinoglenoid notch to innervate the infraspinatus.
• Thus, if injury occurs distal to the spinoglenoid notch, only the infraspinatus will show abnormalities, as the supraspinatus is already innervated at that point.
• If the injury to the suprascapular nerve occurs proximal to the spinoglenoid notch, then both supraspinatus and infraspinatus should show abnormalities.
• Upper trunk plexopathy would also show abnormalities in the deltoid (normal in our patient’s study).
• C5 radiculopathy would also show abnormalities in the deltoid and cervical paraspinals (normal in our patient’s study).
The lateral antebrachial cutaneous nerve (LAC) arises in which of the following ways?
A None of these answers is correct
B As a direct branch of the lateral cord of the brachial plexus
C As the continuation of the musculocutaneous nerve
D As a direct branch of the medial cord of the brachial plexus
Answer: C
Explanation:
• Lateral antebrachail cutaneous nerve (LAC) is actually just the terminal portion of the musculocutaneous nerve, after it has innervated all its muscles.
Which of the following structures does not belong within the anterior compartment of the lower leg?
A Extensor digitorum longus
B Tibialis anterior
C Deep fibular nerve
D Superficial fibular nerve
Answer: D
Explanation:
• Superficial fibular nerve lies within the lateral compartment of the lower leg.
• It innervates the fibularis longus and brevis of the lateral compartment.
In a nerve conduction study, the _______ is _______ charged, thus attracting _______ towards it.
A Cathode, positively, negative ions
B Cathode, negatively, positive ions
C Anode, positively, negative ions
D Anode, negatively, positive ions
Answer: B
Explanation:
• On the stimulating electrode during a nerve conduction study, the cathode is negatively charged, which attracts positive sodium ions towards it.
• These sodium ions accumulate right outside the axon membrane where their concentration becomes so large that they trigger the voltage-gated sodium channels to open, thus initiating an action potential.
You are performing an EMG on a patient with hand numbness. NCS reveals prolonged latency of the SNAP (sensory nerve action potential) to digit 2 and the CMAP to the abductor pollicis brevis (APB). The SNAP to digit 5 and the CMAP to the abductor digiti minimi are normal. Needle EMG reveals 1+ fibrillations in the APB and flexor carpi radialis (FCR). The remaining muscles, including deltoid, brachioradialis, flexor carpi ulnaris, first dorsal interosseus, and cervical paraspinals, are normal. What is the most likely etiology of this condition?
A Compression between the two heads of the flexor carpi ulnaris (FCU)
B Compression underneath the flexor retinaculum
C Compression underneath the ligament of Struthers
D Compression within the Arcade of Struthers
Answer: C
Explanation:
• Median neuropathy at the elbow (due to active denervation observed in the flexor carpi radialis (FCR), a median nerve muscle located at the elbow).
○ This can be caused by compression of the median nerve by a tight pronator teres muscle, bicipital aponeurosis, or ligament of Struthers, all in the elbow.
• Arcade of Struthers and the two heads of the flexor carpi radialis (FCR) can compress the ulnar nerve and cause ulnar neuropathy at the elbow.
• The normal ulnar nerve studies in this case rule out these answer choices.
• Compression of the median nerve under the flexor retinaculum causes median neuropathy at the wrist, but the +1 fibs and sharps in the FCR rule out median neuropathy at the wrist as the most likely cause of this patient’s symptoms.
All of the following muscles are hip extensors except which of the following?
A All of the listed muscles are hip extensors
B Gluteus medius
C Semitendinosus
D Gluteus maximus
Answer: A
Explanation:
• All of these muscles have fibers which cross the hip joint on the posterior aspect of the body, rendering them all with some degree of hip extension function.
During an upper limb EMG/NCS you detect normal sensory nerve action potentials (SNAPs) to digits 1,2, and 5. Compound muscle action potentials (CMAPs) to the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) are normal. Needle EMG to the deltoid and teres minor shows decreased recruitment and 3+ positive sharp waves, while the biceps brachii, triceps, pronator teres, FDI, and APB are normal. Which of the following is most likely associated with this condition?
A Improper use of crutches
B Myokymia
C Spiral groove of humerus fracture
D Winged scapula
Answer: A
Explanation:
• The needle EMG results localize this injury to the axillary nerve (axillary neuropathy), which innervates the deltoid and teres minor.
• These muscles demonstrate active denervation in this study, indicative of axonal loss.
• Improper crutch use can cause axillary neuropathy.
• A posterior cord plexopathy would produce abnormal EMG in the triceps, so the lesion is more distal, i.e. in the axillary nerve.
• A CMAP to the deltoid would be abnormal in our patient as well, but that is not mentioned in our patient’s study.
• Winged scapula is associated with long thoracic neuropathy and spinal accessory neuropathy.
• Spiral groove fractures cause radial neuropathy.
• Myokymia is seen in upper trunk brachial plexopathy.
A patient’s left upper limb EMG/NCS results are as follows. Sensory nerve action potentials (SNAPs) of the median nerve to the thumb and ulnar nerve to digit 5 are prolonged. EMG reveals decreased recruitment and 3+ fibrillations in pectoralis major, flexor digitorum superficialis, flexor carpi ulnaris, abductor pollicis brevis, and first dorsal interosseous, but normal activity in deltoid, biceps, brachioradialis, triceps, and extensor indicis proprius. Which of the following EMG/NCS findings would you also expect to find in this patient?
A None of these answers is correct
B Decreased amplitude of medial antebrachial cutaneous nerve SNAP
C Normal EMG of FD profundus to digits 2 and 3, but abnormal activity in FDP to digits 4 and 5
D Prolonged latency of lateral antebrachial cutaneous nerve SNAP
Answer: B
Explanation:
• Medial cord brachial plexopathy, as all medial cord muscles are affected, with median and ulnar SNAPs (medial cord) being affected as well, but radial SNAP being normal (posterior cord).
• The lateral antebrachial cutaneous nerve SNAP would be normal in a medial cordopathy, as the lateral antebrachial cunateous nerve arises from the musculocutaneous nerve, which arises from the lateral cord of the brachial plexus
• The entire FDP to digits 2-5 is all medial cord-innervated.
• “Decreased amplitude of the medial antebrachial cutaneous nerve SNAP” is the best answer choice, as the medial antebrachial cutaneous nerve (MAC) arises from the medial cord of the brachial plexus, and would be expected to be abnormal in this patient.
All of the following are hip flexors except which muscle?
A Iliopsoas
B Rectus femoris
C Sartorius
D Tensor fascia lata
Answer: D
Explanation:
• Tensor fascia lata’s function is hip abduction and internal rotation. The remaining muscles are hip flexors.
All of the following muscles are flexors of the shoulder except…?
A Pectoralis major
B Biceps brachii
C Posterior deltoid
D Anterior deltoid
Answer: C
Explanation:
• Posterior deltoid is a shoulder extensor - NOT a flexor.
Which of the following muscles is not an elbow flexor?
A Pronator teres
B Brachialis
C Biceps brachii
D Coracobrachialis
Answer: D
Explanation:
• Coracobrachialis is a shoulder flexor, NOT an elbow flexor.
• The remaining muscles cross the elbow joint on the anterior surface of the body, thus rendering them elbow flexors.
In a Klumpke palsy, which of the following electrodiagnostic findings would most likely be present? SNAP: sensory nerve action potential. PIP: proximal interphalangeal joint.
A Negative “OK” sign
B Sensory loss of lateral forearm
C Intact PIP flexion strength
D Normal median nerve SNAP to the thumb
Answer: D
Explanation:
• Klumpke palsy (lower trunk brachial plexopathy) is a C8-T1/lower trbunk plexopathy.
• Thus, downstream nerves and muscles will be affected, including all intrinsic hand muscles, flexor digitorum superficialis and profundus, flexor carpi ulnaris.
• Sensory loss occurs in the medial arm, medial forearm (MAC territory), and hand (excluding the median nerve’s C6 fiber innervation of the thumb territory - hence the normal median SNAP to the thumb).
• Flexor digitorum superficialis is affected, thus causing weak PIP flexion strength.
• The lateral antebrachial cutaneous nerve (LAC) is innervated by C5-C6 upper trunk fibers; thus, lateral forearm sensation would be normal in this case.
• The “OK” sign is an anterior interosseous nerve test, whose muscles involve C8 and T1 innervation; thus, the “OK” sign would be expected to be positive in this case.
○ The Froment sign is an observable sign that correlates with the complaint of a weakened ability to pinch normally between the first and second digits. This sign is sometimes elicited by asking the patient to grasp a piece of paper between the thumb and index finger.
You are performing an EMG on a patient with hand numbness. You note prolonged latency of the sensory nerve action potential (SNAP) to digit 5. The compound motor action potential (CMAP) to the abductor digiti minimi (ADM) is normal when stimulating at the wrist, but reduced when stimulating above the elbow and near the axilla. What is the next best step?
A None of these answers is correct
B Perform median nerve conductions
C Stimulate below the elbow
D Proceed to needle EMG
Answer: C
Explanation:
• This question demonstrates low CMAP amplitude when stimulating proximally, but normal when stimulating distally, indicating that conduction block is taking place somewhere between the above-elbow stimulation site and the wrist.
• The next best step would be to stimulate below the elbow and see if the amplitude is normal again.
• If normal, then you have confirmed a conduction block somewhere at the elbow (between the above-elbow site and below-elbow site).
• If abnormal, then the conduction block is somewhere in the forearm between the below-elbow site and the wrist.
• If abnormal, again, this can also be a Martin-Gruber Anastomosis, the normal anatomic variant by which median nerve fibers cross over into the ulnar nerve somewhere in the forearm to supply innervation to the ulnar nerve muscles of the hand.
○ In case of MGA, record over the abductor digiti minimi (as you are doing) and stimulate the median nerve at the elbow, and see if the amplitude is repaired in your “conduction block”.
○ If all of the amplitude is repaired, then you have MGA, and not conduction block of the ulnar nerve.
You are reviewing EMG/NCS results of the right lower limb. The superficial fibular sensory nerve action potential (SNAP) is abnormal while the sural SNAP is normal. Needle EMG reveals decreased recruitment and +1 fibrillations in the fibularis longus and normal activity in tibialis anterior, extensor digitorum brevis, abductor hallucis, gastrocnemius, medial hamstrings, rectus femoris, tensor fascia lata, and lumbar paraspinals. Which of the following is the most likely diagnosis?
A Deep fibular neuropathy
B Superficial fibular neuropathy
C Proximal sciatic neuropathy
D Distal sciatic neuropathy
Answer: B
Explanation:
• Superficial fibular neuropathy is the best answer.
• Sciatic neuropathy would involve the gastrocnemius and abductor hallucis, as well as tibialis anterior and extensor digitorum brevis theoretically, which are all spared here.
• Deep fibular neuropathy would spare the fibularis longus and affect the tibialis anterior and extensor digitorum brevis.
Which nerve is most susceptible to injury in an anterior hip dislocation?
A Lateral femoral cutaneous nerve
B Superior gluteal nerve
C Sciatic nerve
D Femoral nerve
Answer: D
Explanation:
• Femoral nerve is the key nerve to worry about in the setting of anterior hip dislocations.
• Sciatic nerve is most likely to be injured in a posterior hip dislocation.
• Lateral femoral cutaneous nerve is most likely to be injured in the setting of extreme weight changes, tight clothes/garments/belts, and diabetes.
Which peripheral nerve innervates the bladder to stimulate bladder emptying via detrusor contraction?
A Parasympathetic chain
B Pudendal
C Pelvic
D Hypogastric
Answer: C
Explanation:
“Parasympathetics Pee Pelvic”: the pelvic nerve carries parasympathetic fibers which innervate the detrusor muscle, which then contracts to cause bladder emptying.
A 28 year-old male presents for a right upper limb EMG/NCS. During the study you detect decreased amplitude of the sensory nerve action potential (SNAP) to the anatomic snuffbox, with normal SNAPs to digits 2 and 5. Compound motor action potentials (CMAPs) to the extensor indicis proprius (EIP), abductor pollicis brevis (APB), and first dorsal interosseous (FDI) are normal. Needle EMG of the cervical paraspinals, deltoid, biceps brachii, triceps, brachioradialis, EIP, APB, and FDI is normal. Which of the following is the most likely cause of the patient’s symptoms?
A Improper crutch use
B Midshaft humerus fracture
C Compression by the Arcade of Frohse
D Tight wristwatch
Answer: D
Explanation:
• Cheiralgia Paresthetica - essentially superficial radial neuropathy, a pure sensory syndrome, hence the abnormal radial SNAP (snuffbox SNAP) but normal CMAPs and needle EMG.
• A tight wristwatch, or handcuffs, or procedural trauma, could cause injury to the superficial radial nerve, thus causing pain over the radial nerve territory of the hand.
• This can be detected by abnormal SNAPs to the anatomic snuffbox and radial SNAP to digit 1 (the thumb).
• Midshaft humerus fractures classically produce radial neuropathy that spares the triceps and anconeus (as these muscles are innervated prior to the humeral midshaft area - the spiral groove) but shows abnormalities in other downstream radial nerve-innervated muscles.
• Improper crutch use can cause a proximal radial neuropathy, but that would demonstrate EMG abnormalities in the triceps/anconeus, and the triceps is normal in this patient’s study.
• Compression by the Arcade of Frohse can cause posterior interosseous neuropathy (PIN-opathy) - a pure motor neuropathy that would spare brachioradialis (not a PIN-innervated muscle) and show normal radial SNAPs (our radial SNAP in this patient’s study is abnormal).
The plantaris muscle is contained within which of the following lower leg compartments?
A Anterior
B Lateral
C Deep posterior
D Superficial posterior
Answer: D
Explanation:
• The superficial posterior leg compartment contains the gastrocnemius, soleus, and plantaris muscles.
Which of the following muscles is the primary flexor of the elbow?
A Coracobrachialis
B Brachioradialis
C Biceps brachii
D Brachialis
Answer: D
Explanation:
• Brachialis is the main elbow flexor.
• Biceps brachii and brachioradialis do contribute to elbow flexion, but not as much as brachialis.
• Coracobrachialis does NOT flex the elbow.
The rhomboids are innervated by which trunk of the brachial plexus?
A None of these answers is correct
B Lower
C Middle
D Upper
Answer: A
Explanation:
• Rhomboids are innervated by C4, C5 dorsal scapular nerve.
• This occurs just proximal to the brachial plexus - thus, NO trunks or cords are involved in their innervation.
You are reviewing EMG/NCS results of a patient. You notice prolonged latency, decreased conduction velocity, increased temporal dispersion, and normal amplitude on NCS. There is decreased recruitment on EMG. Which of the following conclusions is most likely correct?
A Axonal loss without conduction block
B Axonal loss with conduction block
C Demyelination without conduction block
D Demyelination with conduction block
Answer: D
Explanation:
• Demyelination is the stripping of the myelin sheath around axons. As myelin increases conduction velocity of axons (decreasing their latency), removal of this myelin will cause slowed conduction velocity, prolonged latency (it takes a longer time for the action potential to reach the recording electrode), and increased temporal dispersion.
• Temporal dispersion is the widening of the SNAP or CMAP due to impulses reaching the recording electrode at widely varying times (due to demyelination decreasing the uniformity of signal transmission along a nerve’s axons).
• Amplitude decrease occurs with axonal loss.
• Normal amplitude in the setting of decreased recruitment suggests conduction block.
• Decreased amplitude with decreased recruitment suggests axonal loss.
When performing an ultrasound-guided corticosteroid injection into the 1st extensor compartment, which of the following is the most likely potential complication?
A Superficial radial nerve injury B Posterior interosseous nerve injury C Ulnar nerve injury D Anterior interosseous nerve injury
Answer: A
Explanation: • Superficial radial nerve runs right along the 1st extensor compartment, and is susceptible to stretching/compression/crush if not identified and accounted for prior to advancing the needle towards the 1st extensor compartment (which contains APL and EPB tendons). • This procedure is commonly done for De Quervain Tenosynovitis.
The muscles of the anterior compartment of the lower leg generally perform which of the following functions?
A Dorsiflexion and toe extension
B Plantarflexion and inversion
C Toe flexion and inversion
D Plantarflexion and eversion
Answer: A
Explanation:
• The primary purpose of the muscles of the anterior compartment is to dorsiflex the ankle and extend the toes.
• The tibialis anterior does also have some secondary inversion action.
A 72 year-old male is currently being treated in the ICU for urinary tract infection (UTI) leading to sepsis. Having survived the infection, the patient is ordered physical therapy (PT). However, the patient is unable to participate in PT, citing profound weakness and numbness/tingling. He denies a history of this problem. You are called to perform an EMG/NCS to discover the cause of the patient’s symptoms. You decide to study the right hemibody. NCS reveals normal latencies, but decreased amplitude of median, ulnar, radial, tibial, and fibular SNAPs and CMAPs (sensory nerve and compound motor action potentials). EMG reveals long-duration, large amplitude motor units with decreased recruitment and 2+ fibrillations extensor digitorum brevis, abductor hallucis, tibialis anterior, and first dorsal interosseous. Which of the following is the most likely diagnosis?
A Critical illness neuropathy
B Diabetic polyneuropathy
C Critical illness myopathy
D Chronic inflammatory demyelinating polyradiculopathy (CIDP)
Answer: A
Explanation:
• Critical illness neuropathy (CIN) usually involves a history of a critical illness, typically a sepsis/SIRS scenario, and as the patient recovers from the medical aspects of this, they begin to complain of new-onset profound weakness with numbness/tingling.
○ CIN is an axonal sensorimotor polyneuropathy; thus, it will decrease the amplitudes of both SNAPs and CMAPs while leaving the latency/conduction velocity largely intact.
○ EMG shows a neuropathic recruitment pattern (long-duration, large amplitude units with decreased recruitment; the axonal loss causes the active denervation reflected as fibrillations and positive sharp waves).
• Critical illness myopathy presents classically as proximal>distal weakness in a critical illness setting with normal sensation and normal SNAPs, and short-duration, small amplitude, early recruitment motor units on EMG.
• Diabetic PN manifests chronically in patients with diabetes, not acutely in the ICU setting. CIDP presents much more gradually as well.
