2 - EDX Study Flashcards
What is NCS study ๐
Studies that assess the ability of peripheral nerves to conduct electrical impulses, in which waveform is generated and its parameters are evaluated to monitor peripheral neuronal function.
What is the purpose of electrodiagnosis soon after nerve injury ? ๐๐
๐ก The larger the distal CMAP the better the prognosis.
To distinguish neurapraxia from axonotmesis or neurotmesis by examining the amplitude of the distal CMAP:
- Neurapraxia the distal CMAP is maintained
- Axonotmesis or neurotmesis the distal CMAP disappears after 10 days as a result of Wallerian degeneration.
In general, demyelination injury have better prognosis due to the ability to re-myelinate via shwan cells.
PMR Secrets 3rd Edition Chapter 15 EDX pg133
5 Limitations of EDX study (Objection)
- Highly deepened on technician technique and artifacts (cold temp and electric noise).
- Examine large fibers only, small fibers not included.
- Not reliable for proximal muscles
- NCS evaluate lesions distal to DRG, not proximal (proximal will be normal)
- Needle EMG evaluate small type 1 motor units which are recruited earlier. While larger motor units with later recruitment are not measured.
PMR Secrets 3rd Edition Chapter 15 EDX pg127
List & Define 5 parameters in NCS. ๐๐
1- Conduction velocity
Speed an impulse travels along a nerve
Dependent on the integrity of the myelin sheath.
Normal values are >50 m/sec in the upper limbs and >40 m/sec in the lower limbs.
2- Onset Latency
Time required for an electrical stimulus to initiate an action potential.
Recorded at the initial deflection from baseline
3- Peak latency
Time required for electrical stimulus to result in peak of the amplitude.
Dependent on the myelination of a nerve
Recorded at the peak of the waveform response
4- Amplitude
Maximum voltage difference between two points
From baseline to negative peak (called Baseline to Peak)
From first negative peak to the next positive peak (called Peak to Peak)
5- Duration
Initial deflection from baseline to the first baseline crossing.
Cuccurollo 4th Edition Chapter 5 EDX pg352
Compare Sensory nerve studies (SNAP) and Motor nerve studies (CMAP)
Sensory nerve studies (SNAP)
Measure conduction of an impulse along sensory nerve fibers by using microvolt ( ยตV )
Sensory cell bodies are located in Dorsal root ganglion (DRG)
Motor nerve studies (CMAP)
Measure conduction of an impulse along motor unit by using millivolt ( mV )
Motor cell bodies are located in Anterior horn cell (AHC)
Cuccurollo 4th Edition Chapter 5 EDX pg356-357
Explain how can you identify post and pre-ganglionic lesions ๐๐
- Postganglionic injury
Wallerian degeneration of both motor and sensory axons โ CMAP and SNAP diminished or absent.
- Preganglionic injury
Sensory fibers to remain in contact with their cell body in DRG โ Normal SNAPs
Motor fibers will be separated from anterior horn cells โ diminished CMAP
Cuccurollo 4th Edition Chapter 5 EDX pg356
Patient with low CMAPs, give 4 DDx. ๐๐
๐ก Think anatomy: Axon, NMJ or muscle or could be entrapment.
- Axonal neuropathy
- Conduction block
- NMJ disorders
- Myopathies
Fig 3.16. Patterns of nerve conduction abnormalities A, B, C, D.
A. Normal Study
B. Axonal Loss โ Low Amp, Minimal changes in Latency and CV.
C. Demyelination โ Slow CV and Prolonged Latency, Normal Amp
D. Demyelination with conduction block & temporal dispersion. (GBS)
List 2 direction of recording used in NCS study ๐
Orthodromic Recording
Action potential is recorded traveling in the direction of its typical physiologic conduction
- Orthodromic sensory fibers travel toward the spinal cord
- Orthodromic motor nerve study records AP impulses traveling toward the spinal cord
Antidromic Recording
Action potential is recorded traveling in the opposite direction of its typical physiologic conduction.
- Antidromic sensory study records sensory impulses traveling away from the spinal cord.
- Antidromic motor nerve study records AP impulses traveling toward the spinal cord
Cuccurollo 4th edition Chapter 5 EDX pg337-8
Compare H Reflex & F Wave. Anatomy - Record Site - Stimulation Threshold - Indication - Limitation
Cuccurollo 4th Edition Chapter 5 EDX pg359
Patient with foot drop. What is the significance of A Wave in his NCS?
This waveform represents recovery by collateral sprouting following nerve damage due to a previous denervation and reinnervation process
Time of A Wave: Between CMAP and F Wave
So its found in antidromic stimlation
Cuccurollo 4th Edition Chapter 5 EDX pg360
What is the result of blink reflex study in facial nerve lesion?
REFLEX
- Afferent Sensory branches of CN V (trigeminal nerve)
- Efferent Motor branches of CN VII (facial nerve)
FACIAL PALSY
Same side stimulation โ Abnormal Ipsilateral R1 & R2
Opposite side stimulation โ Abnormal contralateral R2
Cuccurollo 4th Edition Chapter 5 EDX pg362
What is the result of blink reflex study in trigeminal nerve lesion?
REFLEX
- Afferent Sensory branches of CN V (trigeminal nerve)
- Efferent Motor branches of CN VII (facial nerve)
TRIGEMINAL PALSY
Abnormal study (right and left, early and late response) in stimulated side only.
Cuccurollo 4th Edition Chapter 5 EDX pg362
Explain Blink Reflex ๐
Blink Reflex Arc Pathways:
- Afferent Sensory branches of CN V (trigeminal nerve)
- Efferent Motor branches of CN VII (facial nerve)
Stimulated Nerve: ipsilateral supraorbital nerve
Recorded Muscle: orbicularis oculi muscles
Response:
- Ipsilateral R1 (Early) Through the pons
- Bilateral R2 (Late) Through the pons and lateral medulla โ Blink reflex
Clinical indication of NCS in facial palsy? ๐๐ Dr. Jamal
Poor outcomes if:
- Axonal injuries.
- Absence of an evoked potential in 7 days.
- CMAP <10% of the unaffected side
Recovery > 1 year
Cuccurollo 4th Edition Chapter 5 EDX pg363
Pons come before medulla, so R1 (pons) R2 (medulla)
If all is affected then is systemic condition โ Demyelinating peripheral polyneuropathy
F. Lesion in pons
G. Lesion in medulla
H. Demyelination
Cuccurollo 4th edition Chapter 5 pg362
What is Synkinesis? ๐
๐ก After facial nerve injuries leading, reinnervation might be to inappropriate muscles which result in lip twitching when closing an eye or crocodile tears when chewing.
Figure 1. Oculo-oral synkinesis: (A) voluntary eye closure on the left and an involuntary movement of the oral commissure on the non-paralyzed side due to aberrant activity of the buccinator muscle. (B) Injection points: Lateral portion and pre-tarsal region of Orbicularis oculi; Depressor labii inferioris and lip elevatorsโzygomatic major and minor, levator labii superioris and levator labii superioris alaeque nasi. (C ) Clinical result 15 days after Botulinim toxin type A (BoNT-A) injection.
https://www.mdpi.com/2072-6651/13/2/159/htm
List 4 types of surface electrodes ๐๐ Dr. Jamal
- Disposable strip electrode
- Cup or flat disc electrode
- Circular ground electrode
- Wire ring electrode
- Standard bar electrode
Cuccurollo 4th Edition Chapter 5 EDX pg347
Stimulation Intensity. Which one is used in EDX study? ๐๐ Dr. Diaโa
Threshold stimulus
Electrical stimulus level that is just enough to produce detectable action potential.
Submaximal stimulus
Electrical stimulus level just below maximal level and above threshold level.
Low prolonged amplitude (impression of axonopathy and conduction block)
Maximal stimulus
Electrical stimulus level which added stimulus donโt result increase in action potential
Supramaximal stimulus
๐ก Electrical stimulus at 20% above the maximal stimulus and is typically used for NCS.
Cuccurollo 4th Edition Chapter 5 EDX pg349
With stimulus intensity set too high or too low, unwanted results may occur. Explain. ๐
Too Low
- Falsely lower recorded amplitude
- Falsely prolonged latency
- False impression of an axonopathy or conduction block.
Too High
- Decreased conduction times
- Shortened latencies
- Altered waveforms
- Amplitudes remain unchanged
Cuccurollo 4th Edition Chapter 5 EDX pg349
List 2 ways to minimize stimulus artifact and ensure accurate result while conducting NCS ๐
๐ก Proper technique of hand preperation and electrode placement
- Cleansing the skin from dirt, perspiration, and lotions
- Appropriate anode and cathode placement
- Placing the ground electrode between the recording electrode and stimulator
High vs Low pass filter
Cuccurollo 4th Edition Chapter 5 EDX
Temperature effect. Mention at what temperature ๐๐ COMMON EXAM
Everything will increased expect for velocity, slow n cold (30 LL 32 UL).
Cuccurollo 4th ed - Chapter 5 EDX pg354
Electrode Separations <4 cm Apart
Mimics AXONOPATHY
Cuccurollo 4th Edition Chapter 5 EDX 356
List 2 causes of initial positive deflection.
- Inappropriate placement of the electrodes
- Volume conduction from other muscles or nerves
- Anomalous innervations
Cuccurollo 4th Edition Chapter 5 EDX 357
List two contraindications for EDX study
- External cardiac pacemakers
- Central line catheters
Cuccurollo 4th Edition Chapter 5 EDX pg352
Patient on anti-platelet and anticoagulant, should they stop their meds?
Not routinely encouraged to hold anticoagulant or antiplatelet medications for this study.
Caution
- Platelet counts <50,000 per microliter
- INR acceptable at 3.0.
Cuccurollo 4th Edition Chapter 5 EDX pg351
List 2 causes of falsely decreased amplitude.๐
Which technical problems can result in inaccurate results?
- Submaximal stimulation
- Stimulating over thickened skin from callous formation or edema
- Active and reference electrodes should not be too close together <4cm apart.
๐ก Cold hand will increase amplitude
Cuccurollo 4th Edition Chapter 5 EDX pg357
PMR Secrets 3rd Edition Chapter 18 pg155
Define Temporal dispersion
Temporal dispersion
Difference in CV of the fastest and slowest nerve fibers. High difference result in waveform spreading out (disperses):
(I) Fast conduction axon
(II) Medium conduction axon
(III) Slow conducting axon.
What is Somatosensory evoked potential (SSEP)? Indications? Limitation?
Somatosensory evoked potential (SSEP)
Study evaluating ascending sensory pathways using an afferent potential which travels to spinal root, spinal cord (posterior column), contralateral medial lemniscus, thalamus, to the somatosensory cortex.
Nerves
- Median for the upper limb
- Tibial nerve for the lower limb.
Indications
- Peripheral nerve injuries
- CNS (brain, brainstem, spinal cord) lesions such as multiple sclerosis (MS)
- Intraoperative monitoring of spinal surgery.
Limitation
- Only evaluates the nerve fibers sensing vibration and proprioception (posterior column)
- Evaluates a long neural pathway, which may dilute focal lesions and hinder specificity of injury location
- Affected by sleep and high doses of general anesthetics
Cuccurollo 4th edition Chapter 5 EDX pg364-366
Patient did NCS recently, but didnโt do and EMG in his case.
What are the clinical indications for ordering an EMG?
What more benefits can we get? Is EMG helpful in EDX? or NCS is enough?
๐ก in EMG, common interpretations are: Fibs, PSW, recruitment and MUAP shape.
- Localize lesion in the roots, trunks, cords, or distal branches of the plexus by testing different muscles of same origin nerve/root.
- Looking for signs of axonal damage or deinnervation (fibrillations and positive sharp waves) which help in determining the prognosis and assess the severity of damage.
- Differentiate neuropathic from myogenic disorders (MUAP wave form)
Neurology Secrets 6th Edition Chapter 32 EDX
What is EMG? ๐
Needle EMG
A recording needle electrode is placed into a muscle to evaluate nerve and muscle function.
Parameters
- Insertional activity
- Resting activity
- Voluntary recruitment
Cuccurollo 4th edition Chapter 5 EDX pg366
Draw & Define Motor Unit Action Potential (MUAP). Draw. 5 marks. ๐๐
๐ก MUAP read in reverse
Recording (AP) from muscle fibers from single motor unit (MU) , by using needle electrode.
1- Amplitude
Represent muscle fibers recorded near the needle electrode.
From the most positive to the most negative peak.
- Increased from a reinnervation process (neuropathic MUAP)
- Decreased from loss of muscle fibers (myopathic MUAP)
2- Phase
Represent synchronicity of muscle fiber APs firing
3- Rise time
Represents proximity of the needle to the motor unit
Time from MUAP baseline to the peak of the negative wave.
4- Duration
Represent number of muscle fibers within the motor unit.
From initial deflection from baseline to its final return
- Long duration: neurogenic condition (collateral sprouting)
- Short duration: mayopathic condition (less muscle fibers)
5- Turn/Serrations
Changes in the direction of the waveform that do not cross the baseline
Normally โค 4, Polyphasicity if โฅ 5
Causes: Muscle fiber dropout, alterations in fiber conduction velocity, or reinnervation from collateral sprouting.
Cuccurollo 4th Edition Chapter 5 EDX pg375
1- Normal
2- Long-duration, large-amplitude (LDLA) polyphasic potentials
Denervation and reinnervation from collateral sprouting causes increased number of muscle fibers per motor unit. Seen in neuropathic diseases > myopathic disease.
3- Short-duration, small-amplitude (SDSA) polyphasic potentials
Dysfunction of muscle fibers seen in myopathic diseases and NMJ disorders > severe neuropathic injury
Cuccurollo 4th edition Chapter 5 EDX pg376
Unstable MUAP: Variations in the MUAPโs amplitude, duration, and slope.
Commonly seen in NMJ disorders, which cause irregular blocking of discharges
Cuccurollo 4th Edition Chapter 5 EDX pg376
Giant potential, associated with polymyositis
Cuccurollo 4th Edition Chapter 5 EDX pg376
List 2 reasons why EMG result were inaccurate. ๐๐
- Cold temperature
- Inaccurate electrode separation
- Submaximal stimulation
- Interference from near by electric source
Define insertional activities ๐๐
What causes increased or decreased insertional activities?
Insertional Activities
Normal discharge potentials that are mechanically provoked by physically disrupting the muscle cell membrane with a needle electrode.
Increased (dying or de-innervation )
- Irritable cell membrane: Neuropathic and myopathic conditions
- Active denervation
Decreased (Dead or barrier around)
- Muscle atrophy
- Ischemia
- Fat
- Edema
- Electrolyte abnormalities
Cuccurollo 4th Edition Chapter 5 EDX pg366
List two normal spontaneous activities. ๐
Miniature Endplate Potential (mEPP) โEnd Plate Noiseโ
Monophasic negative potentials
Occur spontaneously at the NMJ, and are referred to as endplate noise. They result from the normal spontaneous exocytosis of individual quanta of ACh (100โ200 quanta) traveling across the NMJ every 5 seconds, leading to a nonpropagated, subthreshold endplate potential.
Endplate Potential (EPP) โEnd Plate Spikeโ
Biphasic single muscle fiber AP
Increased ACh release, provoked by needle irritation of the muscle fiber or synchronization of several MEPPs resulting in single muscle fiber AP
Cuccurollo 4th Edition Chapter 5 EDX pg367
Why does Abnormal Spontaneous Activity occur? ๐
List 4 abnormal spontaneous activities related to Muscle fibers or LMN pathology ๐๐
Abnormal Spontaneous Activity
Nerve resting membrane potential (RMP) becomes less negative and unstable, causing it to approach the threshold more easily to activate an AP.
TL;DR Spontaneous AP due to low resting membrane potential
Why itโs easier to become positive? because muscles ares less negative.
Abnormal spontaneous activities related to Muscle fibers or LMN pathology
- Fibrillation (Fibs)
- Positive Sharp Waves (PSWs)
- Complex repetitive discharges (CRDs)
- Myotonic discharges
Cuccurollo 4th Edition Chapter 5 EDX pg367
FIBs
Spontaneous depolarization (AP firing) of single denervated muscle fibers from uncontrolled ACh release.
Can be found in neuropathies as well as myopathies.
ACh hypersensitivity: after injury, there is increase production of ACh receptors so we have reduced depolarization threshold
PSW
Spontaneous depolarization of single muscle fibers consist of sharp initial deflection from baseline then return to baseline.
Cuccurollo 4th Edition Chapter 5 EDX pg368-369
PMR Secrets 3rd Edition Chapter 15 EDX pg128
Complex repetitive discharges (CRDs)
Form of communication within the nervous system involving the coupling of adjacent (touching) nerve fibers caused by the exchange of ions between the cells, or as a result of local electrical fields, but distinct from direct communication systems such as synapses.
ุดูู ู ู ุฃุดูุงู ุงูุงุชุตุงู ุฏุงุฎู ุงูุฌูุงุฒ ุงูุนุตุจู ุงูุฐู ูุชุถู ู ุงูุชุฑุงู ุฃููุงู ุนุตุจูุฉ ู ุฌุงูุฑุฉ (ู ูุงู ุณุฉ) ูุงุชุฌุฉ ุนู ุชุจุงุฏู ุงูุฃูููุงุช ุจูู ุงูุฎูุงูุง ุ ุฃู ููุชูุฌุฉ ูู ุฌุงูุงุช ููุฑุจุงุฆูุฉ ู ุญููุฉ ุ ูููููุง ุชุฎุชูู ุนู ุงูุฃูุธู ุฉ ุงูู ุจุงุดุฑุฉ ู ุซู ููุงุท ุงูุงุดุชุจุงู ุงูุนุตุจู.
Theory 1 (Ephaptic Activation)
CRD is depolarization of a single muscle fiber followed by ephaptic spread to adjacent denervated fibers (direct spread from muscle membrane to muscle membrane) resulting in a circus movement (primary loop).
Shapiro Electromyography and Neuromuscular Disorders - 4th Edition (2020)
Direct activation by local electrical current of group of adjacent muscle fibers seen in both neuropathic and myopathic
PMR Secrets Chapter 15 EDX pg129
Theory 2 (Collateral Sprouting)
Denervated muscle fibers are reinnervated by collateral sprouting from axons of a neighboring motor unit, so population of muscle fibers now belonging to one motor unit lacks neural control resulting in muscle fibers lie in close proximity to each other and serve as a circuit for the pace maker fiber.
Hallmark sign is regular interval between each discharge
Cuccurollo 4th Edition Chapter 5 EDX pg369-370
Myotonic Discharges
Biphasic single muscle fiber APs triggered by needle movement, percussion, or voluntary contraction. Caused by alteration of ion channels in the muscle membrane and can be seen with or without clinical myotonia.
Characterized by waxing and waning of both amplitude and frequency.
Cuccurollo 4th Edition Chapter 5 EDX pg370
List 3 abnormal spontaneous activities related to Motor unit ๐๐
- Fasciculation potentials
- Myokymic discharges
- Neuromyotonic discharges
Cuccurollo 4th Edition Chapter 5 EDX pg368
Fasciculation
Spontaneous discharges originating from the motor neuron or its axon resulting in intermittent muscle fiber contraction.
Its visible to naked eyes, also can be felt by the patient, its not just single muscle fibers like fibrillation, its motor unit or its axon firing those group of muscle fibers.
๐ก Remember its under abnormal spontaneous activity of MOTOR UNIT!
Benign
Normal motor examination
Not associated with muscle weakness, atrophy, or reflex abnormalities
Pathological
Abnormal motor examination
If associated with FIBs or PSWs
Cuccurollo 4th Edition Chapter 5 EDX pg371
Myokymic discharges, define & where itโs commonly seen? ๐
๐ก Remember its under abnormal spontaneous activity of MOTOR UNIT!
Rhythmic groups of MUAPs firing repetitively, clinically presents as slow continuous muscle fiber contractions.
Common in radiated-induced neuropathy
Cuccurollo 4th Edition Chapter 5 EDX pg372
List 4 causes of facial myokemia ๐ ๐
- Multiple Sclerosis
- Brainstem neoplasm
- Polyradiculopathy
- Bellโs palsy
Cuccurollo 4th edition Chapter 5 EDX pg371
Neuromyotonic discharges, define & where itโs commonly seen?
Neuromyotonic discharges
Damaged peripheral motor axons result in high-frequency, repetitive discharges with progressively decremental amplitudes originating due to individual muscle fiber fatigue and drop off.
๐ก Remember its under abnormal spontaneous activity of MOTOR UNIT!
- Nerve disorder: Neuromyotonia, chronic neuropathic disease, tetany
- Toxins: Anticholinesterase
Cuccurollo 4th Edition Chapter 5 EDX pg373
List 2 causes of extremity myokemia
- Radiation plexopathy (most common)
- Compression neuropathy
- Rattlesnake venom
Cuccurollo 4th Edition Chapter 5 EDX pg372
What is cramp discharge? Where can be seen?
Cramp Discharge
Painful involuntary muscle contraction, followed by relaxation
MAPs
- Normal morphology
- High frequencies
- Irregular
Causes
- Electrolyte disturbances
- Uremia
- Pregnancy
- Myxedema
- Strenuous exercises
- Prolonged muscle contraction
- Liver cirrhosis
- Myotonia congenita
- Myotonic dystrophy
- Stiff-manโs syndrome.
Cuccuroll 4th Edition Chapter 5 EDX pg373
Define Recruitment, List 2 abnormal MUAP recruitment pattern ๐
Recruitment
Ability to add successive motor units to increase the force of a contraction.
CNS can increase the strength of muscle contraction by:
- Increasing the number of active motor units (ie, spatial recruitment)
- Increasing the firing rate (firing frequency) at which individual motor units fire to optimize the summated tension generated (ie, temporal recruitment)
Early recruitment (myopathic)
๐ก Neighboring motor units are called early to help early in contraction
Early firing of many MUAPs with a mild contraction, seen in myopathic conditions and NMJ disorders leading to less force to be generated per motor unit, thus more motor units are recruited.
Reduced recruitment (neuropathic)
๐ก Weak motor unit, not recruiting enough muscles
Firing fewer than expected MUAPs with even a maximal contraction, seen in neuropathic conditions.
Cuccurollo 4th Edition Chapter 5 EDX pg377
Recruitment Parameters. 3 marks.
- Firing Rate (FR): number of times a MUAP fires per second
- Recruitment frequency (RF) = Number of times a AP fires per second.
- Recruitment interval (RI) = Time between two AP of the same motor unit.
๐ก Memory Aid
RF = Force = less muscles, less force = Reduced in myopathies.
RI = Innervation = less innervation = Reduced in neuropathies.
Myopathic diseases
- Loss of muscle fibers causes early recruitment, means a second motor unit to join in early to help increase contractile force.
- Thus decreased RF since muscle fibers are diseased, leading to increase RI.
Neuropathic disease (On overworked motor unit)
- Loss of motor units limits additional motor unit activation, making it hard to increase contractile force
- Reduced recruitment = we canโt recruit more motor units
- Causes the first motor unit to fire more rapidly (more RF), thus shorten RI.
Cuccurollo 4th Edition Chapter 5 EDX pg377-378
