Lesson 1 Flashcards
A 38-year-old man is referred for evaluation of pain in the left buttocks and hip with numbness along the posterior calf. A left sural nerve response is unobtainable, whereas the right sural nerve
has a distal latency of 3.1 ms and an amplitude of 28 µV. Motor nerve conduction studies are normal for both fibular and tibial nerves. The H wave is recorded at 32.1 ms on the right and at 34.8 ms on the left. Needle electromyography examination shows occasional fibrillation potentials and reduced recruitment in the left biceps femoris, gastrocnemius, and posterior tibialis, and normal findings in the left anterior tibialis, vastus medialis, tensor fascia lata, and lumbar paraspinal muscles. Which of the following is the most likely diagnosis?
A. S1 radiculopathy.
B. L5 radiculopathy.
C. Sciatic neuropathy.
D. Fibular neuropathy.
E. Sural nerve entrapment syndrome.
C
COMMENTARY:
Lumbar radiculopathy is often associated with abnormalities in the paraspinal muscles; fibular neuropathy should spare the biceps femoris and posterior tibialis and should have abnormal fibular
motor nerve conduction studies. Sciatic neuropathy with primarily tibial division involvement best explains the findings.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 24-25.
A post-fixed brachial plexus has contributions primarily from the root levels of:
A. C2-C6.
B. C3-C7.
C. C4-C8.
D. C5-T1.
E. C6-T2.
E
COMMENTARY:
The brachial plexus is termed “post-fixed” when the majority of contribution is from the C6-T2 levels and is termed “pre-fixed” when the majority of contribution is from the C4-8 levels.
REFERENCE(S):
Ferrante M. Brachial plexopathies: classification, causes, and consequences. Muscle Nerve 2004;30:547-568.
Which one of the following best describes fasciculation potentials?
A. Rapidly firing, high-amplitude, polyphasic motor unit action potentials (MUAPs).
B. Trains of motor unit potentials under voluntary control.
C. Spontaneous, irregular firing of MUAPs.
D. Semirhythmic grouped discharges.
E. Same significance as positive sharp waves.
C
COMMENTARY:
Fasciculation potentials are the electrically summated voltage of depolarizing muscles fibers belonging to one motor unit. Their discharge rate (1Hz to many per minute) is irregular and involuntary control. Their waveform morphology has the same characteristics as those of a simple motor unit or polyphasic action potentials with respect to amplitude, duration and phases. Fasciculation potentials may be seen in normal individuals as well as in a variety of disease states and thus may be associated with or without fibrillations and positive waves. Semirhythmic grouped discharges are characteristic of myokymic discharges.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd edition. Philadelphia: Hanley & Belfus? 2002. p 251.
A 28-year-old tennis player complains of pain and weakness in the forearm. Sensation in the hand is normal, but there is weakness of interphalangeal flexion of the thumb. The median-to-index finger
sensory response is normal. Needle electromyography (EMG) of the abductor pollicis brevis is normal. What should be done next?
A. Diagnose mild carpal tunnel syndrome.
B. Diagnose thoracic outlet syndrome with neurapraxia.
C. Perform a needle EMG examination of the extensor indicus and paraspinal muscles.
D. Perform a needle EMG examination of the flexor pollicis longus and pronator quadratus muscles.
E. Perform nerve conduction studies of the radial nerve.
54: D
COMMENTARY:
The patient has weakness of flexor pollicis longus, with no sensory symptoms. This muscle is innervated by the median nerve through the anterior interosseous nerve. This muscle with the pronator quadratus (and the median portion of flexor digitorum profundus) should be sampled by needle electromyography.
The median distal latency is normal and not compatible with carpal tunnel syndrome. Neurogenic thoracic outlet does not usually cause forearm muscle weakness. The radial-innervated muscles and
conduction studies are not necessary.
REFERENCE(S):
Brown WF, Bolton CF. Clinical electromyography, 2nd ed. Boston: Butterworths; 1993. p 230
Which is the most critical factor listed in assessing heart rate variability during cyclic deep breathing?
A. Age.
B. Height.
C. Core body temperature.
D. Calculation used or statistical method.
E. Time of day.
A
COMMENTARY:
Heart responses to deep breathing progressively decline with age. Normal values are age stratified. Other factors listed have no measurable or lesser effects on responses.
REFERENCE(S):
Low PA, ed. Clinical autonomic disorders: evaluation and management, 2nd ed. Philadelphia: LippincottRaven; 1997. pp 186-187, 193.
Which muscle listed is most clinically useful for a needle electromyography examination in a patient with hoarseness?
A. Mylohyoid.
B. Genioglossus.
C. Cricothyroid.
D. Lateral pterygoid.
E. Masseter.
C
COMMENTARY:
Needle electromyography is the only routine electrodiagnostic medicine technique to evaluate hoarseness. The cricothyroid muscle, innervated by the superior laryngeal nerve, is most easily tested.
REFERENCE(S):
Dumitru D. Electrodiagnostic medicine. Philadelphia: Hanley & Belfus; 1995. pp 718-719.
When the sweep speed set at 10 ms/div and 10 div on the screen, a single voluntary motor unit action potential (MUAP) appears once per sweep on the screen. The MUAP slowly moves toward the right with each sweep. What is the frequency of the MUAP?
A. 1 Hz.
B. 8 Hz.
C. 10 Hz.
D. 12 Hz.
E. 100 Hz.
B
COMMENTARY:
Setting the screen with 10 ms/div and 10 div on the screen results in total screen sweep of 100 ms. If a single motor unit action potential remained stationary on the screen during subsequent discharges, the
discharging rate is 10 Hz. If it slowly moves to the right, the discharging rate is slower than 10 Hz.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle; principles and practice, 4th ed. New York,
Oxford University Press; 2013. pp 339-347.
What is a miniature endplate potential?
A. The response of an individual muscle fiber to acute denervation.
B. The presynaptic axon terminal response to near depletion of acetylcholine.
C. The response of the endplate to full nerve terminal depolarization.
D. The endplate response to the spontaneous release of acetylcholine.
E. Electric activity recorded from the muscle spindle.
D
COMMENTARY:
Miniature endplate potentials are the postsynaptic muscle fiber potentials produced through the spontaneous release of individual quanta of acetylcholine from the presynaptic axon terminals. Such
potentials are characteristically monophasic, negative, of relatively short duration (less than 5 ms) and have amplitudes less than 20 µV.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 19-20.
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. p 909.
A 45-year-old man presents with tingling in the middle and index fingers of the right hand. Nerve conduction studies are normal. Needle electromyography (EMG) in the triceps and pronator teres
show fibrillation potentials and reduced recruitment. Needle EMG in the biceps, deltoid, and first dorsal interosseous muscles are normal. Where is the lesion?
A. C8 nerve root.
B. Radial nerve at the spiral groove.
C. Median nerve at the wrist.
D. C7 nerve root.
E. Posterior cord brachial plexus.
D
COMMENTARY:
Needle electromyography abnormalities localize to the C7 nerve root. A posterior cord brachial plexopathy would involve the deltoid muscle.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 462.
During muscle contraction, the formation of the bridges between the actin and myosin depends on:
A. Sodium (Na).
B. Potassium (K).
C. Calcium (Ca).
D. Chlorine (Cl).
E. None of the above.
C
COMMENTARY:
On a molecular level, muscles contract when links or bridges form between the myosin heads and the actin filaments, and the myosin heads tilt while linked to the actin filaments. The bridges between
myosin heads and actin form only when tropomyosin, a component of the actin filament, changes position so as to expose “active sites” (“active” means it has a high affinity to bind with myosin heads)
on the actin filament so that myosin heads can bind to actin. The tropomyosin’s change in position is caused by the presence of Ca++, and this Ca++ binds to another component of the actin filament,
troponin. The troponin molecule has 3 globular protein components: troponin I, T, and C. Troponin T attaches to tropomyosin, while troponin C has a high affinity for Ca++. In physiologic muscle
contractions, the source of this Ca++ is Ca++ which has been released from the T tubules of the sarcoplasmic reticulum when a muscle action potential arrives and the membrane of the T tubule
depolarizes.
REFERENCE(S):
Dumitru D. Electrodiagnostic medicine. Philadelphia: Hanley & Belfus; 1995. pp 22, 24-26.
Following 1 minute of contraction during needle electromyography of the gastrocnemius, there is an abrupt onset of a large number of potentials firing at 50 Hz for 20 seconds; just before termination they fire irregularly. This most likely represents:
A. Cramp potentials.
B. Complex repetitive discharges.
C. Myokymic discharges.
D. Fasciculation potentials.
E. Electrode artifact.
A
COMMENTARY:
A cramp potential is the product of multiple motor units firing synchronously, typically between 40-60 Hz. They typically are painful and involve large areas of the muscle. The calf muscle is a common site of cramping after exercise (muscle activation). Cramps can occur in normal individuals or in some specific disease states.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 281.
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. p 356.
A 65-year-old male presents with a 3-year history of progressive muscle weakness. Examination shows weakness of the deep finger flexors, quadriceps, and ankle dorsiflexors. His creatine kinase is elevated to 900 U/L. Muscle biopsy of the left quadriceps is most likely to show which of the following pathological findings?
A. Angular muscle fibers with fiber type grouping.
B. Enlarged capillaries with complement deposited in capillary walls adjacent to myofibers.
C. Perifascicular atrophy with tubuloreticular inclusions in endothelial walls on electron microscopy.
D. Necrotic muscle fibers with scant inflammatory cells.
E. Muscle fibers with rimmed vacuoles with amyloid deposition and increased COX negative fibers.
E
COMMENTARY:
Clinical history of an elderly male with subacute progressive weakness with preferential involvement of deep finger flexors and quadriceps is most suggestive of sporadic inclusion body myositis. The pathological findings seen in this disease include rimmed vacuoles with amyloid deposition and increased COX negative fibers. The other choices represent muscle pathology findings in a neurogenic process (A), myopathy with necrosis and pipestem capillaries (B), dermatomyositis (C), and necrotizing myopathy (D).
REFERENCE(S):
Amato AA, Russell JA. Neuromuscular disorders, 2nd ed. New York: McGraw-Hill; 2016. pp 233-260, 681-700.
While your patient gradually increases the voluntary tension in the muscle undergoing testing, you notice that the early motor unit action potential you have been observing is present 4 times per
sweep and is accompanied by 1 other potential per sweep. The best explanation (gain 200 µV/div, 10 ms/div sweep speed, 10 divisions per screen) is that this represents:
A. Normal recruitment and “psychogenic” weakness.
B. Increased (early) recruitment as seen in a myopathy.
C. Decreased (reduced) recruitment as seen in a neuropathy.
D. Decreased (reduced) recruitment as seen in an upper motor neuron syndrome.
E. Insufficient information for assessing recruitment.
C
COMMENTARY:
This description of waveforms portrays rapid and reduced recruitment as seen in denervation (C). Normally, the first recruited unit will fire at approximately 10 Hz (the recruitment frequency) when a second unit is recruited. When the firing frequency is approximately 20 Hz, 4 or more motor units will be active. In this instance, the first unit is firing more rapidly (40 Hz) with only a single other unit recruited. In “psychogenic” weakness (A) and upper motor neuron syndrome (D), few motor units may be firing, but firing frequency is not rapid. In myopathic weakness (B), greater than normal numbers of units are recruited (early recruitment) for a given force generated.
REFERENCE(S):
Daube JR. Electrodiagnosis of muscle disorders. In: Engel AG, Franzini-Armstrong C, eds. Myology, 2nd ed. McGraw-Hill: New York; 1994. p 764.
Which types of waveforms associated with hyperventilation may be seen by a needle electromyography examination?
A. Doublets.
B. Fibrillations.
C. Complex repetitive discharges.
D. Myokymic discharges.
E. Positive sharp waves.
A
COMMENTARY:
Multiple discharges can be seen with hyperexcitability of the motor neuron pool. Hyperventilation, latent tetany, and other metabolic states can cause this.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 2nd ed. Boston: Butterworth-Heinemann; 2005. pp 209-210.
An electrodiagnostic study may proceed without consent only when:
A. The individual is incompetent to consent.
B. Evaluating newborns for pathology.
C. The patient is in a clinical emergency and is critically ill.
D. The patient has no primary care physician.
E. The patient is well known to the examiner.
C
COMMENTARY:
During a medical emergency, if a patient is unable to give consent and no surrogates can be contacted, standard of care treatment may be performed on the basis of presumed consent. A surrogate will be
required for patients that are incompetent. Newborns will require their parent or guardian’s consent. Lack of a primary care physician and a well-known patient do not absolve the physician’s duty to
properly inform the patient of the potential risks and benefits of the procedure.
REFERENCE(S):
Leonard J, Abel N, Cochrane T, Denys E, Goldman E, Muscik D, Simpson D, Swisher K; American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM). Guidelines for ethical
behavior relating to clinical practice issues in neuromuscular and electrodiagnostic medicine. Muscle Nerve 2010;42(4):481.
What effect would raising the low-frequency (high pass) filter up to 50 Hz with a constant high frequency filter cutoff have on nerve conduction studies with respect to duration and amplitude parameters of a compound muscle action potential?
A. No change would occur.
B. This would shorten the duration and lower the amplitude.
C. This would lengthen the duration and lower the amplitude.
D. This would shorten the duration and increase the amplitude.
E. This would lengthen the duration and there would be no change in amplitude.
B
COMMENTARY:
The low-frequency (high pass) filter cutoff removes the lower frequencies, allowing only the high frequencies to be observed. The recommended low-frequency cutoff for nerve conduction studies is 2-10 Hz, while the high-frequency cutoffs for sensory nerve action potentials (SNAPs) and compound muscle action potentials (CMAPs) are 2000 and 10,000 Hz, respectively. The effect of raising this low frequency filter cutoff while keeping the high-frequency filter constant would result in both SNAPs and CMAPs exhibiting lower amplitude, shorter peak latencies with a shorter duration and greater phase accumulation, with CMAPs being more affected than SNAPs.
REFERENCE(S):
Koo YS, Cho CS, Kim B-J. Pitfalls in using electrophysiological studies to diagnose neuromuscular disorders. J Clin Neurol 2012;8(1):1-14.
Which of the following findings would be most likely seen in a patient with active polymyositis?
A. Long duration, large amplitude polyphasic motor units, predominantly in distally sampled muscles.
B. Long duration, large amplitude polyphasic motor units, predominantly in proximally sampled muscles.
C. Short duration, small amplitude polyphasic motor units, predominantly in distally sampled muscles.
D. Short duration, small amplitude polyphasic motor units, predominantly in proximally sampled muscles.
E. Short duration, large amplitude polyphasic motor units, predominantly in proximally sampled muscles
D
COMMENTARY:
In active polymyositis, one typically finds short duration, small amplitude polyphasic motor units (“myopathic units”), predominantly in proximally- as opposed to distally-sampled muscles. Long
duration, large amplitude polyphasic units are more commonly seen in neuropathic processes.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 2nd ed. Boston: Butterworth-Heinemann; 2005. p 582.
Which of the following studies is most likely to be normal in an S1 radiculopathy?
A. Sural sensory nerve action potential.
B. Needle electromyography of the medial gastrocnemius muscle.
C. Tibial-to-abductor hallucis (AH) compound muscle action potential (CMAP) amplitude.
D. Tibial-to-AH F-wave latency.
E. H-wave latency.
A
COMMENTARY:
Sensory nerve conduction studies should be normal in radiculopathy, as the compression is proximal to the dorsal root ganglia. All the other tests described all evaluate the S1 motor nerve root or both motor and sensory nerve roots (H wave).
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 452.
Which of the following is an example of a presynaptic neuromuscular junction disorder?
A. Myasthenia gravis.
B. Primary myopathy.
C. Lambert-Eaton myasthenic syndrome.
D. Anticholinesterase toxicity.
E. Acetylcholine receptor deficiency.
C
COMMENTARY:
Lambert–Eaton myasthenic syndrome, an autoimmune or paraneoplastic disorder, is often associated with small cell lung carcinoma. Antibodies are directed against voltage-gated calcium channels of the presynaptic terminal. Prior to exercise, a low amplitude compound muscle action potential (CMAP) is obtained. After brief, maximal exercise, facilitation is observed with a dramatic increase in CMAP amplitude. However, in the case of myasthenia gravis (MG), a decrement in amplitude with slow repetitive stimulation is observed, which repairs after exercise. MG results from antibodies interfering with the function of the postsynaptic neuromuscular junction. Acetylcholine receptor deficiency and
anticholinesterase toxicity are directed at the postsynaptic region.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 1162.
A previously healthy 54-year-old male develops severe burning pain in his fingertips and numbness in his feet with profound fatigue and mild cardiomyopathy over the last 4 months. He has suffered
with impotence for 1 year, and he now has recurrent diarrhea. There is no history of diabetes; he has a normal fasting glucose and no known toxic exposure. Nerve conduction testing shows absent
sensory potentials in the lower extremities and severe bilateral carpal tunnel syndrome. Which of the following tests will be most likely abnormal and diagnostic?
A. Serum levels of vitamin B12 and methylmalonic acid.
B. Glucose tolerance test.
C. Rectal biopsy.
D. Abdomen and chest computed tomography scan.
E. Cerebral spinal fluid Lyme polymerase chain reaction.
C
COMMENTARY:
Nonhereditary amyloid neuropathy is predominantly sensory with prominent early loss of small fibers, followed by progressive weakness and large-fiber involvement. Dysautonomia is often severe and disabling, as is the pain associated with small fiber damage. Diagnosis depends on the histological demonstration of amyloid either in a rectal or nerve biopsy. Rectal biopsy is positive in 70% of cases, but it must include the submucosa because that tissue is involved more frequently than mucosa.
REFERENCE(S):
Dyck PJ, Thomas PK. Peripheral neuropathy, 4th ed. Philadelphia: Elsevier Saunders; 2005. p 2436.
Oh SJ. Principles of clinical electromyography: case studies. Baltimore: Williams & Wilkins; 1998. p 297.
Which study would be most helpful in differentiating a brachial plexus lesion from nerve root avulsion?
A. H wave from the flexor carpi radialis.
B. F-wave latency measurement.
C. Sensory nerve action potential amplitude.
D. Compound muscle action potential amplitude.
E. Cortical somatosensory evoked response amplitude.
C
COMMENTARY:
The sensory nerve action potential (SNAP) remains normal in lesions proximal to the dorsal root ganglia, including lesions in the nerve roots, whereas plexus or peripheral nerve lesions result in an abnormal SNAP. However, other choices can be abnormal in both cases and may not serve as a criterion for differentiating a plexus from a nerve root lesion.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 2nd ed. Boston: Butterworth-Heinemann; 2005. pp 462-465.
Which neurotransmitter depolarizes the sweat glands?
A. Epinephrine.
B. Acetylcholine.
C. Glycine.
D. Glutamate.
E. None of the above.
B
COMMENTARY:
The neurotransmitter in the sympathetic fibers to the sweat glands is acetylcholine.
REFERENCE(S):
Guyton AC. Textbook of medical physiology, 7th ed. Philadelphia: WB Saunders; 1986. p 852.
Decreasing the inter-electrode distance in a sensory nerve action potential recording will:
A. Increase the amplitude.
B. Decrease the amplitude.
C. Increase the onset latency.
D. Decrease the onset latency.
E. Increase the peak latency.
B
COMMENTARY:
Decreasing the interelectrode distance will have the effect of losing the later portion of the sensory nerve action potential (SNAP) waveform because of premature common mode rejection by the
reference electrode. The displayed waveform is a function of what is seen by the reference electrode subtracted from the active electrode. Therefore, if both see the same waveform simultaneously, there
will be no deflection on the screen. It is only by separating the electrodes spatially and, therefore, temporally that the electrical event of the SNAP can be wholly received by the active electrode before being received by the reference and, therefore, being cancelled out. If the interelectrode distance is decreased, there will be some loss of waveform. This will decrease the amplitude. Also, because it will be the latter aspect of the waveform that is subtracted, the peak will occur earlier and, therefore, peak latency will therefore decrease. Onset latency is not affected.
REFERENCE(S):
Dumitru D, Amato A, Zwartz MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 72-73, 78-79.
Complex repetitive discharges are characterized by which of the following?
A. A gradual onset and slowing of the waveforms.
B. Firing rates ranging from 1-5 Hz.
C. Originating from ephaptic muscle fiber activation.
D. An irregular firing rate of complex waveforms.
E. Appearance in acute neurologic disorders.
C
COMMENTARY:
Complex repetitive discharges (CRDs) typically occur in chronic disorders and fire regularly at rates of 10-100 Hz. They characteristically have an abrupt onset and cessation. CRDs originate from ephaptic transmission between adjacent muscle fibers.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 276-277.
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 4th ed. New York: Oxford University Press; 2013. p 371.
A 62-year-old man with diabetes complains of weakness, fatigue, and lightheadedness upon standing up. He also complains of “numbness” in his feet and a dry mouth. Which one of the following studies would be most helpful in establishing this patient’s diagnosis?
A. Autonomic studies.
B. Needle electromyography (EMG).
C. Repetitive stimulation.
D. Single-fiber EMG.
E. Somatosensory evoked potentials.
A
COMMENTARY:
This patient’s symptoms suggest an autonomic diabetic neuropathy likely associated with a small fiber diabetic neuropathy. Autonomic studies—including quantitative sudomotor axon reflex testing, tilt table testing, deep breathing, and Valsalva maneuver—are most useful, since they assess small fibers and autonomic fibers. Somatosensory evoked potentials may be useful but are mostly used to assess central sensory pathways. Needle electromyography (EMG) assesses motor fibers. Repetitive stimulation and single-fiber EMG are most useful in neuromuscular junction disorders.
REFERENCE(S):
Katirji B, Kaminski HJ, Preston DC, Ruff RL, Shapiro EB, eds. Neuromuscular disorders in clinical practice. Boston: Butterworth-Heinemann; 2002. pp 193-208.
Myotonic discharges primarily in the paraspinal muscles would be most suggestive of:
A. Myasthenia gravis.
B. Myotubular myopathy.
C. Botulinum intoxication.
D. Polymyositis.
E. Acid maltase deficiency.
E
COMMENTARY:
In the adult form of acid maltase deficiency (type 2 glycogenosis), needle electromyographic (EMG) abnormalities—including myotonic discharges and low amplitude, short duration motor unit action
potentials (MUAPs) with early recruitment—may be restricted to the paraspinal, gluteal, and other proximal muscles. Myotonic discharges would not be expected in myasthenia gravis or in botulism.
Myotubular (centronuclear) myopathy may occasionally manifest myotonic discharges, but a predilection for paraspinal involvement has not been described. Although needle EMG abnormalities in
polymyositis may be found predominantly in the paraspinal muscles, these typically include fibrillation potentials and positive sharp waves, complex repetitive discharges, and polyphasic, low amplitude,
short duration MUAPs with early recruitment.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle, 3rd ed. New York: Oxford University Press; 2001. pp 758, 765, 790, 800.
A 66-year-old male presents with bilateral hand weakness and difficulty swallowing. On examination he is noted to have significant finger flexor and mild hip flexor weakness. He has mild atrophy of his biceps, triceps, and intrinsic muscles. Muscle stretch reflexes are normal. No fasciculations are noted. Electrodiagnostic testing is most likely to reveal:
A. Myotonic discharges.
B. Conduction block.
C. Fasciculations.
D. Brief duration, low amplitude motor unit action potentials.
E. Reduced recruitment.
D
COMMENTARY:
Inclusion body myositis (IBM) presents as a slowly progressive weakness and has a predilection for certain muscles (proximal and distal) including iliopsoas, biceps, triceps, and long finger flexors. Needle electromyography frequently shows fibrillations and positive sharp waves in affected muscles. Motor unit action potentials (MUAPs) are often of low amplitude and brief duration with early recruitment, typical of myopathy. Large and long duration MUAPs can be seen in chronic myopathies, particularly IBM.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 421.
Which of the following is true regarding the neuromuscular junction?
A. The postsynaptic membrane is 10 times longer than the presynaptic membrane.
B. Miniature endplate potentials are responsible for muscle action potential.
C. Synaptic transmission, like that of the nerve axon, is bidirectional.
D. Synaptic vesicles contain acetylcholinesterase, an inactive form of acetylcholine (ACh).
E. Each vesicle contains 100,000 molecules of ACh.
A
COMMENTARY:
The synaptic transmission of the neuromuscular junction is unidirectional. Stimulation of the nerve axon, except at the cell body or axon terminal, is bidirectional. Miniature endplate potentials are small depolarizations of the muscle fiber that do not result in muscle action potential. Acetylcholinesterase hydrolyzes acetylcholine (Ach) and is not contained in the vesicles. Vesicles contain 5,000-10,000
molecules of Ach.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 4th ed. New York: Oxford University Press; 2013. pp 432-434.
Which of the following would be most appropriate in the recording of single-fiber potentials for jitter analysis?
A. Positive to negative rise time of greater than 400 µs.
B. Electrode uptake diameter of 1 mm.
C. Electrode impedance greater than that of the amplifier.
D. Peak-to-peak amplitude exceeding 200 µV.
E. Sweep speed of 5 ms/div.
D
COMMENTARY:
In the recording of single-fiber potentials, the single-fiber needle uptake area is 300 µm and recording diameter is 25 µm. One millimeter is the typical uptake area for conventional electromyography (EMG) needles. Acceptable criteria for the recording of a single-fiber potential include a positive-to-negative
rise time of less than 300 µs, an amplitude of at least 200 µV, and an initial sweep speed of 0.5-1.0 ms/div. The sweep speed is later reduced further to improve the resolution of the time locked single fiber pair (for the determination of jitter). Needle EMG recording requires an amplifier impedance significantly greater than the recording electrode in order to maintain a high signal-to-noise ratio.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. Philadelphia: FA Davis; 2001. pp 384-387.
A 36-year-old woman experienced a mild upper respiratory tract infection 10 days ago from which she recovered without sequelae. Yesterday, she awoke with mild low aching back pain and tingling
in her fingers and toes. This morning she awoke with more intense tingling in all extremities, and gait difficulty due to a combination of imbalance and mild weakness of her arms and legs. She presents to the emergency department where her examination is notable for mild diffuse weakness (Medical Research Council grade 4/5 strength) in proximal and distal muscles of all 4 extremities, impaired vibratory sensation in her legs, and absent reflexes throughout. A lumbar puncture is performed and is normal. An urgent electrodiagnostic study is requested. Which of the following findings is most likely to be discovered in this study?
A. Prolongation of tibial H-wave latencies bilaterally.
B. Prolonged motor distal latencies of tibial and fibular nerves.
C. Reduced compound muscle action potential amplitudes of median and ulnar nerves.
D. Increased sensory nerve action potential amplitudes of median and ulnar nerves
E. Presence of fibrillation potentials in distally-sampled muscles.
A
COMMENTARY:
This patient has early Guillain–Barré syndrome, with onset 1 day prior to presentation. The first electrodiagnostic finding seen in this disorder early in the course is abnormal late responses (H wave
and F wave prolongation). The other findings listed are less commonly seen in the acute setting.
REFERENCE(S):
Gordon PH, Wilbourn AJ. Early electrodiagnostic findings in Guillain-Barré syndrome. Arch Neurol 2001;58(6):913-917.
Single-fiber electromyography is abnormal in which of the following conditions?
A. Inclusion body myositis.
B. Amyotrophic lateral sclerosis.
C. Charcot–Marie–Tooth disease.
D. Myasthenia gravis.
E. All of the above.
E
COMMENTARY:
Single-fiber electromyography is used to measure the relative firing of adjacent single muscle fibers from the same motor unit and can detect both prolonged jitter as well as blocking of muscle fibers. Aside from neuromuscular junction transmission disorders, abnormal results can be seen in both nerve and muscle disorders.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 534.
Which of the following is a characteristic of both fibrillations and fasciculations?
A. Regular firing rhythm.
B. An initial negative deflection.
C. Provocation by needle movement.
D. Polyphasic configuration.
E. Spontaneous occurrence.
E
COMMENTARY:
Both fibrillations and fasciculations are spontaneous discharges. Fibrillation potentials have a regular firing rhythm and an initial positive deflection. Fasciculations are irregular in firing. Fibrillations may be provoked by needle movement but fasciculations are not. Fasciculation potentials may be polyphasic but are not necessarily so.
REFERENCE(S):
Daube JR, Rubin DI. Clinical neurophysiology, 3rd ed. New York: Oxford University Press; 2009. pp 425-432.
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 347-356.
An electrodiagnostic (EDX) medicine physician should stop an EDX evaluation if:
A. The physician learns during the examination that the patient has hepatitis C.
B. The patient initially agrees to testing, but later refuses to continue.
C. The physician learns that the patient has no valid insurance.
D. The patient notes that a recent international normalized ratio (INR) was 2.5.
E. The patient is disoriented but a healthcare proxy is available.
B
COMMENTARY:
Prior to performing any electrodiagnostic (EDX) consultation the physician must obtain either verbal or written consent. If informed consent is not given, or is withdrawn during the procedure, the study must cease immediately. The patient’s history of communicable disease and medical insurance should have no impact on the decision to perform an EDX evaluation. Even if the patient’s international normalized ratio is elevated due to warfarin use, EDX evaluation can be safely performed if adequate precautions
are taken and certain vulnerable muscles are avoided. If a patient is confused or disoriented, a healthcare proxy or surrogate should be sought to provide informed consent.
REFERENCE(S):
American Association of Electrodiagnostic Medicine. Guidelines for ethical behavior relating to clinical practice issues in electrodiagnostic medicine. Muscle Nerve Suppl 1999;8:S43-S47.
Which of the following conditions is most likely to clinically mimic lower motor neuron disease?
A. Multifocal motor neuropathy.
B. Lambert-Eaton myasthenic syndrome.
C. Hereditary spastic paraplegia.
D. Cervical myelopathy.
E. Dopa-responsive dystonia.
A
COMMENTARY:
Multifocal motor neuropathy (MMN) is the most common lower motor neuron disease mimic. It is important to differentiate the two as MMN is treatable with intravenous immunoglobulin. It is distinguished by clinical characteristics, electrodiagnostic (EDX) testing, and in some cases, for those who have anti-GM1 antibodies, by serologic testing. Conduction block in motor nerves on EDX testing is a key diagnostic feature of MMN.
REFERENCE(S):
Amato AA, Russell JA. Neuromuscular disorders, 2nd ed. New York: McGraw-Hill; 2016. p 182.
In contrast to the F wave, the H wave:
A. Utilizes a polysynaptic spinal cord reflex arc.
B. Has a maximum amplitude with submaximal stimulation.
C. Has a variable waveform at low rates of stimulation.
D. Can be recorded from stimulation of any nerve/muscle.
E. Depends upon backfiring of motor neurons.
:B
COMMENTARY:
The H-wave amplitude is maximum with submaximal stimulation, in contrast to both the F- and M-wave responses, which require supramaximal stimulation. The H wave arises from a monosynaptic reflex arc and displays a stable amplitude with slow rates of stimulation. The H wave is recorded from the tibial nerve and gastrocnemius and soleus muscles as well as from the median nerve and flexor carpi radialis muscle. Backfiring of motor neurons is the mechanism of the F wave.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 244-249.
A 56-year-old woman presents with weakness and atrophy of her left quadriceps muscle. On her examination, left knee muscle stretch reflex was reduced. Nerve conduction studies of the left fibular and tibial motor nerves and left sural and saphenous nerves are normal. Needle electromyography demonstrates high amplitude, long duration motor unit potentials in the left vastus lateralis and adductor longus muscles. Motor units in the tensor of the fascia lata and tibialis anterior muscles were normal. What is the most likely localization of the lesion in this case?
A. The sciatic nerve proximal to the biceps femoris.
B. The obturator nerve.
C. The L3 nerve root.
D. The L5 nerve root.
E. The femoral nerve.
C
COMMENTARY:
The normal saphenous sensory response and involvement of the adductor longus makes femoral mononeuropathy inaccurate. Normal tensor fascia latae and tibialis anterior examination makes L4 less likely. L3 nerve root lesion can explain the needle examination findings and normal nerve conduction results.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 501.
Which of the following represents the light colored area of myofibrils containing only actin?
A. A band.
B. I band.
C. Z line.
D. H zone.
E. Sarcolemma.
B
COMMENTARY:
Actin and myosin are the major contractile myofilaments within the muscle fiber. When viewed with polarized light, the thick myosin and thin actin filaments interdigitate. Dark “anisotropic” bands, or A bands, appear where actin and myosin overlap. Light areas containing only actin filaments are considered “isotropic” to polarized light, and are called I bands. The H zone is a lighter area within the A
band where actin filaments do not abut. The sarcomere is the functional subunit of the muscle fiber and measures from Z line to Z line.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 22-24.
A patient had the suprascapular nerve completely severed 6 months ago in the course of a surgical procedure. While performing a needle electromyography for other reasons, you decide to examine the infraspinatus muscle. You find motor unit action potentials of normal configuration and recruitment pattern. What is the most likely explanation?
A. The nerve has regenerated.
B. The infraspinatus muscle has anomalous innervation.
C. The needle is in the trapezius.
D. The infraspinatus muscle is not normally innervated by the suprascapular nerve.
E. Conduction block has resolved.
C
COMMENTARY:
When attempting to examine the infraspinatus, if the needle electrode is placed too superficial, it will then be in the trapezius.
REFERENCE(S):
Perotto AO. Anatomical guide for the electromyographer: the limbs and trunk, 5th ed. Springfield: Charles C. Thomas; 2011, p 125.
Varying or unstable motor unit action potentials occur in which of the following?
A. Acute, complete nerve transection.
B. Lambert–Eaton myasthenic syndrome.
C. Neurapraxia.
D. Steroid myopathy.
E. Stroke.
B
COMMENTARY:
Motor unit action potentials (MUAPs) normally have the same amplitude, duration, and configuration with each firing. Fluctuation of any of these variables during repeated discharges of the same MUP is abnormal and produces varying or unstable MUAPs. Varying MUAPs are caused by blocking of the discharge of action potentials of one or a few of the individual muscle fibers comprising the motor unit. In Lambert–Eaton myasthenic syndrome, the action potential does not reach threshold in one or few of the muscle fibers comprising the motor unit.
REFERENCE(S):
Daube JR, Rubin DI. Needle electromyography. Muscle Nerve 2009;39(2):266.
Which of the following disorders is most likely to be associated with normal needle electromyography findings when the study is performed at least 4 weeks after onset of symptoms?
A. Inclusion body myositis.
B. Botulinum toxin overdose.
C. Nerve root avulsion.
D. Brachial plexopathy.
E. Steroid myopathy.
E
COMMENTARY:
Steroid myopathy demonstrates preferential type 2 muscle fiber atrophy. Needle electromyography (EMG) evaluates type 1 muscle fibers and therefore the needle EMG in steroid myopathy is typically
normal. The remainder of the diagnoses would show needle EMG abnormalities in the affected regions.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 1187-1189,1382-1383, 1397-1398.
A 40-year-old woman presents with numbness and pain in the lateral and anterior thigh. A neuropathy of the right lateral cutaneous nerve of the thigh (meralgia paresthetica) is suspected. Which of the following answers best describes the lateral cutaneous nerve of the thigh?
A. It is a pure sensory nerve that is derived from the L2-3 roots.
B. It is a pure sensory nerve that is derived from the L4-5 roots.
C. It is a pure sensory nerve that is derived from the L1-2 roots.
D. It is a mixed sensory and motor nerve.
E. It usually passes over the inguinal ligament.
A
COMMENTARY:
The lateral cutaneous nerve of the thigh (previously known at the lateral femoral cutaneous nerve) is a pure sensory nerve that is derived from the L2-3 roots and emerges laterally from the psoas muscle, and then crosses obliquely toward the anterior superior iliac spine where it passes under the inguinal ligament.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 502.
What is the advantage of a constant current stimulator versus a constant voltage stimulator when performing nerve conduction studies?
A. Constant current stimulators deliver a consistent stimulus current that is impedance dependent.
B. Constant voltage stimulators deliver a consistent current stimulation that is impedance independent.
C. Constant current stimulators deliver a consistent current that is impedance independent.
D. Constant voltage stimulators deliver a varying current stimulus that is impedance dependent.
E. There is no advantage of one system over the other as both deliver a stimulus current.
C
COMMENTARY:
A constant current stimulator is the preferred device for nerve conduction studies as it delivers a consistent stimulus current that is independent of impedance. The voltage across the stimulating electrode adjusts dynamically to maintain a constant current stimulus despite potentially changing skin impedance. A constant voltage stimulator has a fixed voltage output. As such, changes in skin impedance alter the stimulus current level. This can result in inconsistent stimulus intensity and submaximal stimulation.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. p 53.
A 45-year-old man presents with right foot drop. On examination he has weakness of right foot dorsiflexion, inversion and eversion. Ankle plantar flexion, knee flexion, and extension strength are normal. Patellar and Achilles reflexes are normal. Which of the following, is the best diagnosis, reflecting an accurate localization of the lesion?
A. Right fibular neuropathy at the knee.
B. Right sciatic neuropathy.
C. Right L5 radiculopathy.
D. Right S1 radiculopathy.
E. Right tibial neuropathy.
C
COMMENTARY:
The L5 nerve root innervates the tibialis anterior, fibularis (peroneus) longus, and tibialis posterior muscles (among others) and does not mediate the patellar or Achilles reflex. A sciatic neuropathy would
also cause weakness in foot plantar flexion and knee flexion and an abnormal Achilles reflex. An S1 radiculopathy would cause weakness in the foot plantar flexion and an abnormal Achilles reflex. A tibial
neuropathy would cause plantar flexion weakness.
REFERENCE(S):
Stewart JD. Foot drop: where, why and what to do? Pract Neurol 2008;8(3):158-169.
The external anal sphincter can best be relaxed for needle electromyography examination by:
A. Digital stretch with a finger placed in the anal canal.
B. A long exhalation after a deep breath.
C. Having the patient attempt to relax while lying on his or her side.
D. Having the patient attempt to defecate.
E. Having the patient flex the abdominal muscles.
D
COMMENTARY:
Muscular sphincters function by relaxing. In this case, the external anal sphincter relaxes just before and during defecation.
REFERENCE(S):
Warwick R, Williams PL. Gray’s anatomy. Philadelphia: WB Saunders; 1973. p 1294.
Monopolar and concentric needle electrodes have the most similar characteristic in which of the following?
A. Shape of the needle tip.
B. Recorded firing rates.
C. Recorded amplitudes.
D. Recorded motor unit area.
E. Noise.
B
COMMENTARY:
The recording area of the concentric needle, in general, constitutes a very small portion of the motor unit territory. The monopolar needle is noisier than the concentric electrode. The monopolar needle registers an amplitude larger than that of a concentric needle from the same source, although duration and firing rate remain nearly the same. Studies report variable data of the extent of difference in
amplitude and duration when measuring with monopolar or concentric needles.
REFERENCE(S):
Dumitru D, King J, Nandedkar S. Concentric/monopolar needle electrode modeling: spatial recording territory and physiologic implications. Electroencephalogr Clin Neurophysiol 1997;105:370-378.
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 4th ed. New York, Oxford University Press; 2013. pp 35-37.
Nandedkar S, Sanders D. Recording characteristics of monopolar EMG electrodes. Muscle Nerve 1991;14(2):109-112.
Pease W, Bowyer B. Motor unit analysis comparison between concentric and monopolar electrodes. Am J Phys Med Rehabil 1988;67(1):2-6.
Axonotmesis is characterized by which of the following?
A. Loss of axon but retained epineurium continuity.
B. Loss of axon and loss of epineurium continuity.
C. Persistent segmental conduction block.
D. Axonal preservation but Schwann cell injury.
E. Incompatibility with spontaneous recovery.
A
COMMENTARY:
Axonotmesis is characterized by axonal injury leading to Wallerian degeneration but preserved connective tissue layers, including the surrounding endoneurium, perineurium, and epineurium. Loss of
all connective tissue layers is indicative of the most severe grade of injury (neurotmesis) and is incompatible with spontaneous recovery. Recovery is possible if the connective tissue sheath persists despite axonal degeneration. Neurapraxia is characterized by segmental conduction block but minimal inherent axonal pathology, other than intraneural edema and increased pressure in more severe grades.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 786.
Oh S. Clinical electromyography: nerve conduction studies, 3rd ed. Philadelphia: Lippincott, Williams & Wilkins; 2003. pp 803-819.
A 45-year-old man presents with weakness of his right hand. He denies sensory symptoms. Examination shows severe weakness in median-innervated distal hand intrinsic muscles with relative
sparing of ulnar-innervated hand intrinsic muscles. Reflexes are reduced. Antiganglioside antibody titer is elevated. What is electrodiagnostic testing is most likely to reveal?
A. Decreased activation.
B. Early recruitment.
C. Myotonic discharge.
D. Conduction block.
E. All of the above.
D
COMMENTARY:
Nerve conduction studies show evidence of conduction block along motor fibers in multifocal motor neuropathy. The presence of persistent conduction block often signifies that the disorder is a motor neuropathy and not a motor neuron disease. Early recruitment is typical of muscle disease and would not affect muscles of a single nerve. Conditions that cause myotonic discharges would not affect muscles of a single nerve.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 420.
Which of the following is true when performing nerve conduction studies in Lambert–Eaton myasthenic syndrome?
A. Baseline compound muscle action potential (CMAP) is normal amplitude.
B. Slow (2-3 Hz) repetitive nerve stimulation results in an incrementing response.
C. Baseline CMAP is low amplitude.
D. Endplate potential amplitude is normal at baseline.
E. High frequency (rapid, 10-50 Hz) repetitive nerve stimulation is always necessary for diagnosis.
C
COMMENTARY:
The hallmark of presynaptic neuromuscular junction (NMJ) disorders is low compound muscle action potential (CMAP) amplitude at baseline. In Lambert–Eaton myasthenic syndrome, due to an antibody mediated blockage of voltage-gated calcium channels on the presynaptic terminal, fewer than normal acetylcholine (ACh) quanta are released. This results in a baseline endplate potential (EPP) that is low amplitude. EPP is below threshold at baseline in many muscle fibers, thus a muscle action potential is not generated in many muscle fibers; hence, the baseline CMAP will be low. With slow (2-3 Hz) repetitive nerve stimulation (RNS), there is the typical further reduction in ACh quantal release as the immediate stores of ACh quanta are depleted, resulting in a decremental CMAP response. High frequency RNS is only necessary to diagnose a presynaptic NMJ disorder if the patient is unable to perform a brief maximal voluntary contraction due to severe weakness or mental status (infant, coma).
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. pp 54-59.
A patient with progressive sensorimotor neuropathy demonstrates severely and disproportionately prolonged distal motor latencies and diffusely absent sensory nerve action potentials. No site of focal motor conduction block is identified. Which antibodies are most likely to be present in this patient?
A. Acetylcholine receptor antibodies.
B. Myelin-associated glycoprotein antibodies.
C. GM1 ganglioside antibodies.
D. Voltage-gated potassium channel antibodies.
E. Voltage-gated calcium channel antibodies.
B
COMMENTARY:
Antibodies against myelin-associated glycoprotein (anti-MAG) are associated with often severe sensorimotor neuropathy. Most cases with high anti-MAG titers have an underlying paraproteinemia, usually of the immunoglobulin M type. Patients are generally over age 50. Tremor is also common. Electrodiagnostic studies characteristically demonstrate severe distal motor latency prolongation and a lesser degree of conduction velocity slowing and temporal dispersion, but generally no conduction block. The disparity between distal and more proximal slowing can be highlighted with measures that compare distal to more proximal conduction times, including the terminal latency index and residual latency. GM1 ganglioside antibodies are seen in 30-40% of patients with multifocal motor neuropathy.
Conduction block is a characteristic, but not universally present, feature. In addition, sensory responses show minor or no abnormalities but are not absent. Voltage-gated potassium channel antibodies are associated with Isaacs’ syndrome, cramp-fasciculation syndrome and other hyperexcitability syndromes, and limbic encephalitis. Acetylcholine receptor (AChR) antibodies are seen in a majority of myasthenia gravis patients; antibodies to non-neuromuscular junction AChRs are associated with other disorders
such as epilepsy and autonomic neuropathy. Voltage-gated calcium channel antibodies are associated with the Lambert–Eaton myasthenic syndrome.
REFERENCE(S):
Amato AA, Russell JA. Neuromuscular disorders. New York: McGraw Hill; 2008. pp 234-238.
Cocito D, Isoardo G, Ciaramitaro P, Migliaretti G, Pipieri A, Barbero P, Cucci A, Durelli L. Terminal latency index in polyneuropathy with IgM paraproteinemia and anti-MAG antibody. Muscle Nerve 2001;24(10):1278-1282.
Trojaborg W, Hays AP, van den Berg L, Younger DS, Latov N. Motor conduction parameters in neuropathies associated with anti-MAG antibodies and other types of demyelinating and axonal neuropathies. Muscle Nerve 1995;18(7):730-735.
What effect would lowering the high-frequency (low pass) filter down to 500 Hz with a constant low-frequency cutoff on a compound muscle action potential with respect to the parameters of latency and amplitude?
A. This would result in no change in either parameter.
B. This would result in prolonged onset latencies and reduced amplitudes.
C. This would result in shorter onset latencies and increased amplitudes.
D. This would result in shorter onset latencies with no effect on amplitude.
E. This would result in no effect on latencies with reduced amplitudes.
B
COMMENTARY:
Lowering the high-frequency (low pass) filter will result in both sensory nerve action potentials (SNAPs) and compound muscle action potentials (CMAPs) exhibiting amplitude reduction, delayed peak/onset latency, increased duration, and smoother waveforms, with SNAPs being more affected than CMAPs.
REFERENCE(S):
Koo YS, Cho CS, Kim B-J. Pitfalls in using electrophysiological studies to diagnose neuromuscular disorders. J Clin Neurol 2012;8(1):1-14.
Which statement explains why the sensory nerve action potential is usually unaffected with a typical compressive radiculopathy?
A. There is only a small segment of focal demyelination.
B. There is no significant axonal degeneration.
C. The lesion is usually proximal to the dorsal root ganglion.
D. The lesion is usually distal to the dorsal root ganglion.
E. Radiculopathies affect motor fibers only.
C
COMMENTARY:
Sensory responses are almost invariably unaffected in a typical compression radiculopathy because the lesion is proximal to the dorsal root ganglion. Sensory nerve fibers degenerate only in lesions distal to sensory ganglia or in lesions affecting the ganglionic cells themselves (ganglionopathies). Typical compressive radiculopathies are preganglionic lesions and the amplitudes of the sensory nerve action potentials should not be affected even though the patient may have clinically absent or decreased sensation in the corresponding dermatome.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 107-108.
Wilbourn AJ, Aminoff MJ. AAEM Minimonograph #32: The electrodiagnostic examination of patients with radiculopathies. Muscle Nerve 1998; 21(12):1612-1631.
When interpreting repetitive nerve stimulation studies, which of the following is true?
A. The majority of patients with presynaptic neuromuscular junction disorders have normal compound muscle action potentials at rest.
B. At 2-3 Hz stimulation, Lambert–Eaton myasthenic syndrome (LEMS) demonstrates marked increment.
C. Postactivation exhaustion is present in both LEMS and myasthenia gravis (MG).
D. Abnormalities are demonstrated in asymptomatic muscles in MG.
E. Jitter may be increased with LEMS and botulinum toxicity and increases with increased firing rates.
C
COMMENTARY:
Ninety-five percent of patients with Lambert–Eaton myasthenic syndrome (LEMS) and 45% of patients with botulinum toxicity have a decreased compound muscle action potential amplitude at rest. High
frequency repetitive nerve stimulation demonstrates marked increment in LEMS. Abnormalities are typically seen in symptomatic muscles in myasthenia gravis, but may be normal otherwise. Jitter is
increased in LEMS and botulinum toxicity, and decreases with elevated firing rates.
REFERENCE(S):
Dumitru D, Amato A, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 1169.
If an initial positive deflection is seen in the morphology of the response when recording a compound muscle action potential, what would be the most likely cause?
A. The active recording electrode is not placed exactly over the motor point.
B. The stimulus is submaximal.
C. The temperature is too low.
D. The temperature is too high.
E. There is electrical impedance interference.
A
COMMENTARY:
The active electrode (G1) is placed over the motor point, typically located at the center of the muscle belly, while the reference electrode (G2) is placed over the muscles’ distal tendon. Muscle
depolarization occurs first at the motor endplate zone (motor point). If the active recording electrode is not placed over the motor point, the volume-conducted depolarization potential first occurs at a
distance from the recording electrode and is seen as an initial positive deflection. When the depolarization subsequently travels under the electrode, the potential then becomes negative. If a
positive deflection is seen on a motor nerve conduction study, the active electrode has most likely been placed off of the motor point and should be moved until the positive deflection is no longer seen.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. pp 71-89.
Hereditary neuropathy with liability to pressure palsy is characterized by which of the following?
A. Autosomal recessive inheritance.
B. X-linked inheritance.
C. Painful neuropathy.
D. Tomaculae on nerve biopsy.
E. Primarily axonal neuropathy.
D
COMMENTARY:
Hereditary neuropathy with liability to pressure palsy is characterized on nerve biopsy by tomaculae, which are focal globular thickenings of the myelin sheath, resembling sausages. It is autosomal dominant with painless weakness and numbness.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 905.
A 67-year-old with diabetes presents with 3 months of low back pain radiating into the right leg to the foot with paresthesias but no weakness. Her nerve conduction studies (NCSs) demonstrate normal fibular and tibial compound muscle action potentials and absent superficial fibular and sural sensory nerve action potentials on both legs. NCSs in the arm are normal. Needle electromyography demonstrates fibrillation potentials and long duration motor unit action potentials in the extensor digitorum brevis, tibialis posterior, and tibialis anterior muscles. Which of the following muscles, if abnormal, would be most supportive of an L5 radiculopathy?
A. Adductor longus.
B. Gluteus medius.
C. Rectus femoris.
D. Fibularis longus.
E. Medial gastrocnemius.
B
COMMENTARY:
The history is consistent with radiculopathy. The nerve conduction study results can be seen in polyneuropathy from diabetes. Needle examination abnormalities in the extensor digitorum brevis, tibialis posterior, and tibialis anterior could be seen in distal polyneuropathy or L5 radiculopathy. Abnormality in the gluteus medius is the best answer as it may be abnormal in L5 radiculopathy but should be normal in distal polyneuropathy that does not affect the upper limb.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 461.
What are the effects of cool temperature on nerve conduction studies with respect to amplitude and nerve conduction velocity (NCV)?
A. Increased amplitude and increased NCV.
B. Increased amplitude and slowed NCV.
C. Decreased amplitude and increased NCV.
D. Increased amplitude and no change in NCV.
E. Decreased amplitude and slowed NCV.
B
COMMENTARY:
Warming the limb prior to performing nerve conduction studies (NCSs) is absolutely essential. The ideal way is to use a mechanism that is not just surface warming but warms more thoroughly such as a water bath or warming pack from a hydrocollator. Constant temperature monitoring during the study is essential to prevent misdiagnosis based on artefact due to low temperatures resulting in slow nerve conduction velocity, prolonged distal latency, and increased amplitude during NCSs and increased duration of motor unit action potentials during needle examination.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. pp 71-89.
Which of the following is true regarding the external anal sphincter?
A. It receives innervation from the ilioinguinal nerve.
B. It receives innervation via the dorsal rami of S2, S3, and S4.
C. Its motor unit action potentials (MUAPs) are recordable at rest.
D. Its MUAP discharge rate is greatest during sleep.
E. Its mean motor unit duration on needle electromyography is similar to limb muscles.
C
COMMENTARY:
The anal sphincter receives innervation from the pudendal nerve, which is derived from the anterior (ventral) rami of S3, S4, and occasionally S2. The muscle fascicles interdigitate across the midline
resulting in a side-to-side overlap of innervation. Surface studies have shown increased motor unit activity during trunk movements, coughing, and speaking. The anal sphincter demonstrates continuous
tonic activity, with activity absent only during attempted defecation. Motor unit activity is present during sleep, but is decreased compared to during wakefulness. Motor units average between 200-500 µV in amplitude and are shorter in duration than most limb muscles and are in the range of 5-6 ms.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 379-380.
A 48-year-old railroad conductor has difficulty using his ticket puncher with his right hand. He has no sensory signs or symptoms. Examination demonstrates weakness of the adductor pollicis, first dorsal interosseous, but not abductor digiti quinti muscles. Other muscles examined in the right hand and arm are normal. What is the most likely diagnosis?
A. Anterior interosseous nerve lesion.
B. Posterior interosseous nerve lesion.
C. Ulnar nerve lesion at the elbow.
D. Ulnar nerve lesion at the wrist.
E. Medial cord brachial plexus lesion.
D
COMMENTARY:
The ulnar nerve enters the hand through Guyon’s canal at the wrist, which can be a site of ulnar nerve compression and neuropathy. Sensory impairment, if present, spares the dorsum of the hand innervated by the dorsal cutaneous branch, which arises proximal to the wrist. The lesion at the wrist affects the ulnar-innervated hand muscles. The deep and superficial branch of the ulnar nerve may be affected. In this example the deep branch is selectively affected because of the repetitive recurrent pressure from the ticket puncher. Involvement of the superficial branch results in weakness of the palmaris brevis muscle and loss of sensation in the little finger and ulnar half of the ring finger. Ulnar lesions at the elbow affect the dorsal ulnar cutaneous nerve and may involve the flexor carpi ulnaris and ulnar half of flexor digitorum profundus muscle. Anterior interosseous nerve lesions affect the flexor pollicis longus, radial half of the flexor digitorum profundus and pronator quadrates muscles. Posterior interosseous nerve lesions affect radial-innervated muscles distal to the supinator. Medial plexus lesions affect the lower trunk and would also affect the median-innervated hand muscles.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 632-637.
A fibrillation potential is a spontaneous depolarization of a:
A. Sensory receptor.
B. Muscle fiber.
C. Nerve axon.
D. Motor neuron.
E. Distal nerve twig.
B
COMMENTARY:
A fibrillation potential is the action potential of a spontaneously depolarizing single muscle fiber.
REFERENCE(S):
American Association of Electrodiagnostic Medicine glossary of terms in electrodiagnostic medicine. Muscle Nerve 2001;10:S1-S50.
Dumitru D. Electrodiagnostic medicine. Philadelphia: Hanley & Belfus; 1995. p 230.
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 347.
Motor unit action potential morphology is affected by which of the following parameters?
A. Intrafusal fibers.
B. Type 2 muscle fibers.
C. Distance from the needle to the motor unit.
D. Recruitment frequency.
E. Recruitment ratio.
C
COMMENTARY:
The motor unit action potential (MUAP) morphology is dependent upon the quality of myelin and length of axonal twigs, the quality of the neuromuscular transmission and the number of muscle fibers and their size, as well as the proximity of the needle tip to the motor units being analyzed. Standard needle electromyography analyzes only type 1 extrafusal muscle fibers; type 2 fibers are not the first recruited and therefore are not analyzed. Recruitment frequency and ratio are important parameters to analyze but do not contribute to the individual MUAP morphology.
REFERENCE(S):
Daube JR, Rubin DI. Needle electromyography. Muscle Nerve 2009;39(2): 244-270.
Dumitru D, Amato AA, Zwarts MJ: Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus 2002. pp 266-272.
Anti-GQ1b antibodies are frequently detected in which of the following conditions?
A. Miller Fisher syndrome.
B. Ocular myasthenia gravis.
C. Chronic inflammatory demyelinating polyneuropathy.
D. Lambert–Eaton myasthenic syndrome.
E. Paraneoplastic sensory polyneuropathy.
A
COMMENTARY:
Antibodies against GQ1b ganglioside are associated with the Miller Fisher variant of Guillain–Barré syndrome (characterized by gait ataxia, areflexia and ophthalmoparesis) or with Bickerstaff’s encephalitis. Ocular myasthenia gravis is associated with antibodies against the acetylcholine receptor in 50-65% of cases. A characteristic feature of Lambert−Eaton myasthenic syndrome is the presence of antibodies against the voltage-gated calcium channels in more than 90% of patients. Paraneoplastic sensory polyneuropathy is frequently associated with anti-Hu antibodies.
REFERENCE(S):
Kaminski HJ. Myasthenia gravis. In: Katirji B, Kaminski HJ, Preston DC, Ruff RL, Shapiro BE, eds. Neuromuscular disorders in clinical practice. Boston: Butterworth-Heinemann; 2002. pp 916-930.
Madison P, Newsom-Davis J. Lambert-Eaton myasthenic syndrome. In: Katirji B, Kaminski HJ, Preston DC,
Ruff RL, Shapiro BE, eds. Neuromuscular disorders in clinical practice. Boston: Butterworth Heinemann; 2002. pp 931-941.Pestronk A. Autoantibodies and immune polyneuropathies. In: Katirji B, Kaminski HJ, Preston DC, Ruff RL, Shapiro BE, eds. Neuromuscular disorders in clinical practice. Boston: Butterworth Heinemann; 2002. pp 58-73.
What are some methods to reduce electrode impedance mismatch and 60 Hz interference?
A. Clean all dirt and oil from the skin using alcohol or acetone.
B. Apply conducting electrode gel between the skin and electrodes.
C. Place the ground between the stimulating and recording electrodes.
D. Secure the active and reference recording electrodes firmly to the skin
E. All of the above.
E
COMMENTARY:
Care should be taken to prepare effectively to remove any potential risk for artefact altering the results of nerve conduction studies.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. pp 71-89.
A mononeuropathy which produces lateral scapular winging that is at its most prominent during arm abduction would most likely exhibit weakness of which muscle?
A. Serratus anterior.
B. Subscapularis.
C. Infraspinatus.
D. Trapezius.
E. Teres minor.
D
COMMENTARY:
Lateral winging of the scapula is characteristically caused by weakness of the trapezius or rhomboid muscles (or both). The winging is accentuated with arm abduction. Accentuation with forward flexion is characteristic of serratus anterior weakness. Winging from serratus anterior dysfunction becomes more pronounced when the arm is extended in front of the body. Because the serratus anterior normally pulls the scapula forward against the ribs, weakness of this muscle results in the inferior tip of the scapula
being displaced closer to the spine.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 715-716.
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders, 2nd ed. Philadelphia: Butterworth-Heinemann; 2005. pp 508-509.
Stewart JD. Focal peripheral neuropathies, 2nd ed. New York: Raven Press; 1993. pp 88-89.
Which type of traumatic nerve injury is the most severe and carries a poor prognosis without surgical intervention?
A. Neurotmesis.
B. Neurapraxia.
C. Conduction block.
D. Axonotmesis.
E. Segmental demyelination.
A
COMMENTARY:
Neurotmesis, also known as a fifth degree injury in the Sunderland classification, is characterized by complete disruption of the axons, endoneurial tubes, perineurium, and epineurium. In axonotmesis, the axons have been disrupted but a portion of the surrounding stroma remains intact. Neurapraxia and conduction block are characterized by a focal failure of transmission due to focal demyelination. Myelin only injury usually has an excellent recovery in weeks to months.
REFERENCE(S):
Katirji B, Koontz D. Ch 76: Disorders of peripheral nerves. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC, eds. Bradley’s neurology in clinical practice, 6th ed. Philadelphia: Elsevier Saunders; 2012. pp 1915-1918.
Robinson LR. Traumatic injury to peripheral nerves. Muscle Nerve 2000;23(6):863-873.
During needle electromyography, conduction block would be recognized most easily by abnormalities in which of the following parameters?
A. Activation.
B. Insertional activity.
C. Spontaneous activity.
D. Duration.
E. Recruitment.
E
COMMENTARY:
Conduction block will block the action potential from propagating normally through the affected axon. The remaining intact motor neurons and their axons must therefore increase their frequency of firing to produce muscle movement. This will be noted during the needle examination as reduced recruitment. Activation may be impaired with conduction block, but is not specific. Conduction block alone will have normal insertional and spontaneous activity and normal motor unit action potential duration.
REFERENCE(S):
Daube JR, Rubin DI. Needle electromyography. Muscle Nerve 2009;39(2):244-270.
Which of the following is the most desirable technical condition for reliable repetitive nerve stimulation studies of the upper limb?
A. Stimuli must be of long duration and submaximal.
B. Skin temperature should be at least 33°C.
C. The muscle should be allowed to move freely.
D. Low frequency stimulation should be at 5 or 10 Hz.
E. Patients should take edrophonium prior to testing.
B
COMMENTARY:
Submaximal stimulation can give false incremental and decremental responses and should be avoided. Cold temperature diminishes the decrement response and the degree of decrement is enhanced with
warmer limb temperatures. A poorly immobilized limb may give rise to excessive movement artefact and inconsistent responses. Low frequency stimulation frequency should be kept at 2-3 Hz to prevent
calcium accumulation at the presynaptic nerve terminal. Medications such as edrophonium interfere with interpretation by blunting or eliminating the decremental response.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York; Oxford University Press; 2001. pp 258-268.
Oh S. Clinical electromyography: nerve conduction studies, 3rd ed. Philadelphia: Lippincott Williams & Wilkins; 2003. pp 20-22.
In Bell’s palsy, which of the following muscles will demonstrate abnormality with needle electromyography?
A. Medial pterygoid.
B. Lateral pterygoid.
C. Masseter.
D. Temporalis.
E. Frontalis.
E
COMMENTARY:
Frontalis is the only muscle listed that is innervated by the facial nerve, which is involved in Bell’s palsy. All other muscles are innervated by the trigeminal nerve and will not demonstrate abnormality in Bell’s palsy.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. pp 373-374.
Which is true regarding repetitive nerve stimulation in the evaluation of a suspected neuromuscular junction disorder?
A. A normal compound muscle action potential excludes the diagnosis of Lambert–Eaton
myasthenic syndrome.
B. Immobilizing the area of study will degrade the waveform.
C. Temperature must be maintained at 42°C.
D. Cooling of the limb may worsen symptoms in presynaptic disorders.
E. Patients with early stages of botulism may have normal tests.
E
COMMENTARY:
A normal compound muscle action potential (CMAP) does not exclude the diagnosis of Lambert–Eaton myasthenic syndrome (LEMS), some patients may have low normal CMAPs. Failure to immobilize the area of study may result in misleading results. Temperature should be maintained at 32°C. Patients with myasthenia gravis may be more symptomatic as the temperature is increased and patients with presynaptic disorders (e.g., LEMS, botulism, tick paralysis) may improve with cooling. In the early stages, patients with botulism may have normal studies.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 4th ed. New York: Oxford University Press; 2013. pp. 450, 451, 458.
Needle electromyography of which muscle is at highest risk of causing a pneumothorax?
A. Infraspinatus.
B. Posterior head of the deltoid.
C. Supraspinatus.
D. Latissimus dorsi.
E. Teres minor.
C
COMMENTARY:
Sampling of the supraspinatus is believed to have a higher risk of causing a pneumothorax. Some individuals have an anomalously high lung apex that can be entered while studying the supraspinatus,
especially if the muscle is sampled near the midpoint where the supraspinous fossa is narrowest. The muscle can be more safely sampled medially in the supraspinous fossa. Other muscles associated with pneumothorax as a consequence of needle electromyography (EMG) include the diaphragm, serratus
anterior, rhomboids, intercostal muscles, and cervical and thoracic paraspinal muscles. Unexpected chest pain, shortness of breath, or cyanosis following needle EMG are suspicious signs of an induced pneumothorax.
REFERENCE(S):
Al-Shekhlee A, Shapiro BE, Preston DC. Iatrogenic complications and risks of nerve conduction studies and needle electromyography. Muscle Nerve 2003;27(5):517-526.
Why is neuromuscular transmission more likely to be impaired in proximal than distal muscles in myasthenia gravis?
A. The motor units are larger in proximal muscles.
B. Proximal muscles are warmer than distal muscles.
C. More exposure to abnormal serum antibodies occurs in proximal muscles.
D. Proximal muscles are stimulated more often than distal muscles.
E. Proximal muscles are stimulated at faster frequencies than distal muscles.
B
COMMENTARY:
Proximal muscles are more likely to show decremental responses because they are warmer.
REFERENCE(S):
Dumitru D. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. Ch 15. p 559.
Sural nerve biopsy is most diagnostically informative in which condition?
A. Idiopathic painful sensory neuropathy.
B. Multifocal motor neuropathy.
C. Mononeuritis multiplex.
D. Alcoholic polyneuropathy.
E. Guillain–Barré syndrome.
C
COMMENTARY:
Nerve biopsy should be reserved for select cases that have been carefully characterized clinically, electrophysiologically, and by other diagnostic tests and have a reasonable likelihood of demonstrating a diagnostic finding. Many neuropathies, such as alcoholic neuropathy, show nonspecific axonal loss. Idiopathic painful neuropathy may show minimal changes or have findings restricted to small diameter
fibers better assessed by epidermal nerve fiber density counts on skin biopsy. Multifocal motor neuropathy generally shows minimal to no findings in sensory nerves. Chronic demyelinating neuropathies may show evidence of demyelination or onion bulbs but not in the acute stages; the results often add little to the clinical examination and electrodiagnostic studies. However, sural nerve biopsy is diagnostically useful in a variety of specific disorders especially vasculitic neuropathy (the most important cause of mononeuritis multiplex), amyloid polyneuropathy, sarcoidosis, direct lymphomatous invasion, leprosy, certain toxins, and rare hereditary disorders. Even some of these conditions are currently best diagnosed by simpler and less invasive biopsy of non-neurologic tissues or other assays.
REFERENCE(S):
Mendell JR, Kissel JT, Cornblath DR. Diagnosis and management of peripheral nerve disorders. Contemporary Neurology Series #59. Oxford University Press; 2001. pp 97-98.
Said G. Indications and value of nerve biopsy. Muscle Nerve 1999; 22(12):1617-1619.
Which 2 cervical roots are most commonly involved with burners or stingers?
A. C3 and C4.
B. C4 and C5.
C. C5 and C6.
D. C6 and C7.
E. C7 and T1.
C
COMMENTARY:
Burners or stingers are common in athletes, especially football players. They represent a traction, compression, or direct blow to the upper roots of the brachial plexus. Symptoms frequently involve the
C5 and C6 root levels.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 820.
Weinberg J, Rokito S, Silber JS. Etiology, treatment, and prevention of athletic “stingers.” Clin Sports Med 2003;22(3):493-500.
Which of the following types of abnormal spontaneous activity is generated by a single muscle fiber?
A. Fasciculation potential.
B. Myokymic discharge.
C. Neuromyotonic discharge.
D. Myotonic discharge.
E. Cramp discharge.
D
COMMENTARY:
Myotonic discharges are the repetitive firing of a single muscle fiber, typically at a rate of 20-100 Hz with a waxing and waning firing pattern. Fasciculation potentials, myokymic discharges, neuromyotonic discharges, and cramp discharges are types of abnormal spontaneous activity generated by one or multiple motor units.
REFERENCE(S):
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 277-278.
The observation during peripheral nerve ultrasonography of ulnar nerve subluxation / dislocation during elbow flexion is most likely to be associated with which of the following findings on electrodiagnostic testing?
A. Pseudo-conduction block of the ulnar nerve.
B. The presence of a Martin–Gruber (median-to-ulnar) anastomosis.
C. Myokymic discharges within the first dorsal interosseous.
D. Erroneously normal ulnar nerve conduction velocity across the elbow.
E. Conduction block proximal to the ulnar groove.
D
COMMENTARY:
Ulnar nerve subluxation or dislocation during elbow flexion occurs in up to 25% of healthy volunteers. When displaced from its normal location in the ulnar groove around the elbow, measurements used for nerve conduction studies (NCSs) are inaccurate, which leads to erroneous results with the ulnar NCSs. In patients with classic symptoms of ulnar neuropathy at the elbow and normal electrodiagnostic studies, ultrasound to assess for nerve enlargement and subluxation can be of value.
REFERENCE(S):
Walker FO, Cartwright MS. Neuromuscular ultrasound, 1st ed. Philadelphia: Elsevier Saunders; 2011. pp 78-79.
When compared to motor neurons that innervate type 2 muscle fibers, motor neurons that innervate type 1 muscle fibers have a:
A. Faster conduction velocity.
B. Lower threshold for recruitment.
C. Higher firing frequency.
D. Higher frequency of miniature endplate potentials.
E. Larger axon diameter.
B
COMMENTARY:
Motor units that are composed of type 1 muscle fibers have a lower threshold for recruitment compared to type 2 muscle fibers. Type 1 motor units have slower conduction velocities, smaller diameter axons, slower firing frequencies, and lower frequencies of miniature end-plate potentials.
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 291-292.
A patient suffers from quadriceps weakness, and their ipsilateral femoral motor nerve conduction study (NCS) demonstrates diminished amplitude. The saphenous NCS is abnormal. The sartorius, iliopsoas, and vastus medialis muscles are abnormal and adductor longus and tibialis anterior are normal on needle electromyography. What is the most likely diagnosis?
A. Lumbosacral plexopathy.
B. L2-3 radiculopathy.
C. Femoral neuropathy proximal to the inguinal ligament.
D. Femoral neuropathy distal to the inguinal ligament.
E. Saphenous neuropathy.
C
COMMENTARY:
The femoral nerve arises from L2-4 nerve roots through the lumbar plexus. (There are no sacral branches.) An abnormal sensory response argues against radiculopathy. Muscular branches are given off to the psoas and iliacus before the nerve runs beneath the inguinal ligament.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. pp 357-359.
What is the optimal distance between the active and reference electrodes for recording a sensory nerve action potential?
A. 2.0-2.5 cm.
B. 2.5-3.0 cm.
C. 3.0-4.0 cm.
D. 4.0-5.0 cm.
E. 5.0-6.0 cm.
C
COMMENTARY:
The preferred inter-electrode distance between the active and reference recording electrodes for sensory and mixed nerve recordings is 3.0-4.0 cm. The rationale for this recommendation is to maximize the amplitude of the sensory nerve action potential. This distance ensures that depolarization will not occur under both electrodes simultaneously during sensory nerve conduction studies. The relationship between inter-electrode separation and maximal amplitude/rise time is based on the electrical activity a reference electrode records with respect to the active electrode.
REFERENCE(S):
Daube JR, Rubin DI. Clinical neurophysiology, 3rd ed. New York: Oxford University Press; 2009. pp 240-241.
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 542-543.
Which of the following ultrasonographic findings would be most consistent with the diagnosis of carpal tunnel syndrome?
A. Increased nerve anisotropy.
B. Increased nerve vascularity.
C. Decreased thickness of the epineurium.
D. Decreased bowing of the flexor retinaculum.
E. Bifid morphology of the median nerve.
B
COMMENTARY:
Increased nerve vascularity is observed in association with a variety of pathological conditions including carpal tunnel syndrome (CTS), chronic inflammatory demyelinating polyneuropathy, and leprosy. This may be detected using color Doppler imaging, with the presence of blood flow signals in the perineural plexus or intrafascicular vessels indicating hypervascularity of the nerve. Increased bowing of the flexor retinaculum is seen in CTS; anisotropy aids in differentiating between tissue (e.g., nerve and tendon) though is not a reflection of pathology. Choices C and E may increase the risk of development of CTS though are not in themselves diagnostic. Additionally, increased cross sectional area of the median nerve at the wrist and increased wrist-to-forearm ratio is also associated with the sonographic diagnosis of CTS.
REFERENCE(S):
Walker FO, Cartwright MS. Neuromuscular ultrasound, 1st ed. Philadelphia: Elsevier Saunders; 2011. pp 29-31, 74-75.
Acetylcholine is not the neurotransmitter used by:
A. Sympathetic postganglionic fibers to the heart muscle.
B. Sympathetic postganglionic fibers to the sweat glands.
C. Parasympathetic preganglionic fibers.
D. Sympathetic preganglionic fibers.
E. Parasympathetic postganglionic fibers to the bladder.
A
COMMENTARY:
Within the autonomic nervous system, acetylcholine is the neurotransmitter for parasympathetic preganglionic and postganglionic fibers, sympathetic preganglionic fibers, and sympathetic postganglionic fibers to the sweat glands. The neurotransmitter for the postganglionic sympathetic fibers to other organs is norepinephrine.
REFERENCE(S):
Guyton AC. Textbook of medical physiology, 7th ed. Philadelphia: WB Saunders; 1986. pp 686-697.
A 53-year-old man presents with right shoulder weakness. Needle electromyography shows denervation in the right deltoid, rhomboids, and biceps muscles. The right triceps and pronator teres are normal. Where is the lesion?
A. Musculocutaneous nerve.
B. C5 nerve root.
C. C7 nerve root.
D. Lateral cord brachial plexus.
E. Axillary nerve.
B
COMMENTARY:
The correct answer is the (right) C5 nerve root. In axillary neuropathy, the muscles affected would be the deltoid and teres minor muscles. In a C7 nerve root lesion, the axillary and rhomboid muscles would be spared and the triceps and pronator teres would be abnormal. A right lateral cord lesion would not involve the rhomboid muscle. In a musculocutaneous nerve lesion, the deltoid muscle would be spared.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 491.
Which of the findings listed is associated with poor outcome in Guillain–Barré syndrome?
A. Fibrillation potentials observed in lumbar paraspinal muscles.
B. Absent H wave.
C. Absent fibular-to-extensor digitorum brevis F waves.
D. Low amplitude sural sensory response.
E. Low amplitude tibial motor response.
E
COMMENTARY:
Low amplitude distal compound muscle action potentials are associated with poor outcome in Guillain–Barré syndrome. Fibrillation potentials can be observed with minimal axon loss, and without other findings they do not suggest poor outcome. Absent H waves can be seen with demyelination which is not associated with poor outcome. Absent fibular-to-extensor digitorum brevis F waves are a common finding and not associated with poor outcome. A low amplitude sensory response is not associated with poor outcome.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 396.
A neuropraxic lesion of the fibular nerve at the fibular head would be associated with:
A. Normal superficial fibular sensory nerve action potential amplitude.
B. Normal fibular F waves stimulating at the knee and recording at the extensor digitorum brevis (EDB).
C. Prolonged fibular motor distal latency to the EDB.
D. Slowed sciatic nerve conduction velocity across the knee recording from the abductor digiti quinti (pedis).
E. Reduced or absent sural sensory nerve action potential amplitude.
A
COMMENTARY:
Neurapraxia refers to injuries in which function is temporarily abnormal but the structural integrity of the nerve is preserved. Nerve conduction studies reveal conduction block at the site of injury. Evaluations distal to the site of injury causing neurapraxia, including distal motor latency (C) and sensory responses (A and E) are normal. Conduction through the site of injury, including F waves (B) are abnormal.
REFERENCE(S):
Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 3rd ed. Philadelphia: Elsevier Saunders; 2013. p 32.
Seddon HJ. Three types of nerve injury. Brain 1943;66:237.
In comparison to the compound muscle action potential (CMAP) amplitude, the amplitude of the F-wave response:
A. Should be identical.
B. Should be 1-10% of the amplitude of the preceding CMAP amplitude.
C. Should be 2 times the amplitude of the preceding CMAP amplitude.
D. Should be 25-50% of the amplitude of the preceding CMAP amplitude.
E. Should be largest at submaximal stimulation.
B
COMMENTARY:
F waves are generated by an antidromic backfiring of motor neurons. Only a small population of the available motor neurons is activated by the antidromically propagated motor impulses. The F-wave amplitude is 1-3% of the preceding compound muscle action potential amplitude. The reason for the small number of motor neurons’ activation by an antidromic impulse is still rather poorly understood. The recurrent discharges develop in only a limited number of motor units in part because the antidromic impulse fails to enter the somata in some motor neurons, most frequently because of the block at the axon hillock or in the proximal myelinated segment of the axon. The impulse also may abate during the orthodromic propagation of the spike generated in the soma-dendrite membrane because this impulse can travel back (orthodromically) only after the axon hillock recovers from the refractory period induced by the antidromic stimulation.
REFERENCE(S):
Daube JR, Rubin DI. Clinical neurophysiology, 3rd ed. New York: Oxford University Press; 2009. p 521.
Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, 2nd ed. Philadelphia: Hanley & Belfus; 2002. pp 238-244.
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York: Oxford University Press; 2001. pp 440-443.
Short duration motor unit action potentials occur in which of the following scenarios?
A. Chronic remote cervical radiculopathy.
B. Postpolio syndrome.
C. The low frequency filter is set at 500 Hz instead of 10 Hz.
D. Trigeminal neuralgia.
E. Writer’s cramp.
C
COMMENTARY:
Short duration motor unit action potentials (MUAPs) occur as a result of loss of muscle fibers contributing to the MUAP. This occurs in recently reinnervated motor units where few muscle fibers are innervated; in inflammatory myopathies as a result of muscle fiber necrosis, degeneration, or regeneration; in a situation when the low filter setting is elevated from 10 Hz to 500 Hz, and in a severe neuromuscular junction disorder as a result of signal blockade in some of the muscle fibers contributing to the motor unit.
REFERENCE(S):
Daube JR, Rubin DI. Needle electromyography. Muscle Nerve 2009;39(2):264-265.
A 35-year-old man presents with foot drop after prolonged crossing of his legs during an airline flight. You suspect a fibular neuropathy. What is the earliest point in time after onset of weakness
can the motor nerve conduction studies of the fibular nerve provide definitive information regarding whether the foot drop is due to a severe axon loss or neurapraxia?
A. Within 24 hours.
B. 1-3 days.
C. 4-7 days.
D. 10-14 days.
E. 21 days.
D
COMMENTARY:
Conduction along the nerve distal to an axon loss lesion may be preserved for up to 7 days, but by 10-14 days the amplitude of the compound muscle action potential will decrease in proportion to the completeness of the axon loss injury. Performing nerve conduction studies above and below the fibular head prior to that time would disclose an apparent block of conduction, but one would not be able to differentiate a non-continuity block of conduction due to an axon loss lesion from a demyelinating conduction block (neurapraxia).
REFERENCE(S):
Kimura J. Electrodiagnosis in diseases of nerve and muscle: principles and practice, 3rd ed. New York:
Oxford University Press; 2001. pp 9-103.
In a lower trunk brachial plexus lesion, which of the following is most likely to be abnormal?
A. Needle examination of the deltoid muscle.
B. Needle examination of the extensor carpi radialis longus.
C. Medial antebrachial cutaneous response, recording from the forearm.
D. Lateral antebrachial cutaneous response, recording from the forearm.
E. Median sensory response, recording from the thumb.
C
COMMENTARY:
The medial antebrachial cutaneous nerve arises from the lower trunk of the brachial plexus and is frequently affected by lower trunk brachial plexopathies.
REFERENCE(S):
Stewart JD. Focal peripheral neuropathies, 4th ed. West Vancouver: JBJ Publishing; 2010. pp 120-124.
Which of the following pathologic features are typically seen in acetylcholine receptor (AChR) antibody-positive myasthenia gravis?
A. Increased postsynaptic area with more postjunctional folds and reduced synaptic space.
B. Reduction of complement levels in the region of the postsynaptic membrane.
C. Increased numbers of AChRs on the postsynaptic membrane.
D. Reduction in presynaptic calcium channels.
E. Crosslinking of AChR by antibodies, leading to reabsorption by the postsynaptic membrane
E
COMMENTARY:
A number of pathological changes occur in acetylcholine receptor (AChR) antibody-positive myasthenia gravis (MG) including reduction in postsynaptic area with fewer postjunctional folds and increased synaptic space, increase in complement levels, and reduced numbers of AChRs in the postsynaptic membrane. This is due to crosslinking of AChR antibodies which causes a number of processes such as reabsorption by the postsynaptic membrane and complement-mediated destruction. Reduction in presynaptic calcium channels is not seen in MG but is in Lambert–Eaton myasthenic syndrome.
REFERENCE(S):
Amato AA, Russell JA. Neuromuscular disorders. New York: McGraw Hill; 2008. pp 488-489.
