Abnormal EMG Patterns in Disease EMG... · discharge (slow rate 1 -2 hz) ... sampled, with many...
Transcript of Abnormal EMG Patterns in Disease EMG... · discharge (slow rate 1 -2 hz) ... sampled, with many...
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Abnormal EMG Patterns in Disease
Amanda C. Peltier, MD MS October 12, 2013
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Disclosures
n I have no financial relationships to disclose that are relative to the content of my presentation.
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Basic Tenets of EMG n EMG (even more than nerve conduction
studies) is an extension of the physical exam n When in doubt, reexamine the patient (or
check the equipment) n When in doubt, do not overcall n EDX findings should be reported in the
context of the symptoms and referral doctor’s question
n EDX are uncomfortable. Always stop when the patient asks.
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Abnormal Spontaneous Activity n Fibrillation potentials: spontaneous depolarizations n Positive sharp waves: same significance as fibrillation
potentials n Complex repetitive discharges: depolarization of a
single fiber followed by ephaptic spread (muscle membrane to muscle membrane)
n Myotonic Discharge: spontaneous discharge of msucle fiber with waaxing and waning of amplitude and frequency (rate between 20 and 150)
n Fasciculation: Single, spontaneous, involuntary discharge (slow rate 1-2 hz)
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Grading of PSW/fibs
n Very short runs of unsustained P-waves/fibs (<500 ms) should be interpreted as increased insertional activity.
n 1+ fibs/PSW: at least 2 areas of a muscle with sustained fibs/PSWs, clearly defined visually and by audio
n 2+ fibs/PSW: fibs/PSWs present in most areas sampled in a muscle n 3+ fibs/PSW: fibs/PSWs present in nearly all areas of the muscles
sampled, with many PSWs/fibs at each location n 4+ fibs/PSW: complete interference pattern of PSW/fibs
n This grading is helpful to the person hearing your report, but this
does not usually make or break a diagnosis. Severity of lesion is usually higher with higher amounts of active denervation.
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Examples of Abnormal Spontaneous Activity
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Examples of Abnormal Spontaneous Activity
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Examples of Abnormal Spontaneous Activity
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Examples of Abnormal Spontaneous Activity
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Examples of Abnormal Spontaneous Activity
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Pattern of EMG changes in Neuropathic Disorders n Immediate: Morphology normal, recruitment
decreased or absent (depending on severity of injury) n Same pattern seen in demyelinating disorders with
conduction block n 10 days: Spontaneous activity present (wallerian
degeneration has taken place) n After 6 weeks morphology becomes more
neuropathic (remodeling has occurred): n Decreased recruitment, larger amplitude, polyphasic
n Satellite potentials: small, short duration, unstable units time locked to another larger unit
n Nascent units: Small amplitude short duration units with decreased recruitment (recruitment distinguished from myopathic units)
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Radiculopathy
n Typically, sensory nerve studies remain normal, in the relevant dermatome. n Pathology is proximal to the dorsal root
ganglion.
n Motor CMAP amplitudes can be reduced. n EMG findings:
n Active denervation, reduced recruitment in at least 2 anterior myotome muscles innervated by that root, likely with paraspinal active denervation also.
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Plexopathy
n Sensory studies: Most sensitive. n In contrast to radiculopathy, plexopathies should
feature reduced amplitude/absent SNAPs. n In the dermatome affected:
n Upper trunk: median SNAP + musculocutaneous SNAP n Same for Lateral Cord lesions
n Middle trunk: radial SNAP n Same for Posterior Cord lesions
n Lower trunk: ulnar SNAP + medial cutaneous forearm SNAP n Same for Medial Cord lesions
n EMG: can be severely abnormal, with 3-4+ fibs/no motor units or severely reduced recruitment
n Paraspinals classically unaffected.
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Brachial plexus - tips Dorsal scapular nerve arises
at the proximal point of the upper trunk. It innervates rhomboids, which if abnormal suggests a C5 root lesion.
Radial muscles + deltoid suggests a posterior cord lesion
Abnormal distal median and ulnar muscles on EMG, with normal median sensory study suggests medial cord.
Always look at paraspinals to evaluate root lesion (avulsion)
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Motor Neuron Disease
n ALS, SMA, Kennedy’s disease will all have denervation that cannot be explained by 1 or 2 single lesions.
n One must continue to test additional muscles to rule out more systemic illness.
n E.g. CTS with active denervation in the APB prompts evaluation of pronator, FDI, and other proximal muscles.
n El Escorial criteria: 3 regions, each with 2 muscles showing active denervation PLUS UMN findings in 3 regions (usually no EMG correlate for UMN)
n Awaji criteria are similar but allow for fasciculations to count as active denervation
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Chronic Neurogenic Process
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Acute Nerve Injury
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Myopathy
n EMG reports of myopathy should also include the ideal muscle biopsy target (if desired). n Most abnormal muscle, with small motor units, especially if fibs/PSWs
present. Ideally, this would be a vastus, biceps, deltoid, brachioradialis, gastrocnemius, in declining order of preference.
n Some myopathies can involve paraspinal muscles only. Difficult, but possible to bx this site.
n Generally perform EMG on one side only, leaving the contralateral side for biopsy, to avoid EMG needle site affecting the biopsy
n Exception: generally vastus medialis findings are assumed present in vastus lateralis also.
n The specific diagnosis of type of myopathy is rarely obvious from EMG only (e.g. FSHD vs polymyositis).
n Exception: myotonic dystrophy
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Pattern of EMG changes in Myopathic Disorders n Myopathy: number of functioning muscle fibers
decreased—units smaller, shorter duration. n Abnormal firing causes polyphasia n Acute: short duration, small amplitude units with
normal or early recruitment n Chronic: (some denervation often occurs) long-
duration, high amplitude MUAPS can be seen (often with short-duration, small units)
n Recruitment is still normal or early until end stage
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Recruitment: Myopathic Process
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Questions?
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Acknowledgments
n Dr. James Albers: video n Dr. Christopher Lee: slides n Dr. Peter Donofrio: slides