3nd biennial contemporary clinical neurophysiological ... · pdf fileemg report • the...
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3nd Biennial Contemporary Clinical Neurophysiological
Symposium October 12, 2013
Fundamentals of NCS and NMJ Testing
Peter D. Donofrio, M.D. Professor of Neurology
Vanderbilt University Medical Center
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Disclosure Potential Conflict of Interest
• I have no financial relationships to disclose that are relative to the contents of this presentation.
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Goals of EDX Testing
Localization Severity
Nerve NMJ Anterior Horn Muscle
Fiber type Pathology Temporal course
Adapted from fig 1-2, Preston and Shapiro
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What are the indications for electrodiagnostic
consultation/testing? • Suspected neuromuscular disease
– Anterior Horn Cell Disorders – Nerve root pathology – Peripheral nerve/plexus pathology – Neuromuscular junction pathology – Muscle pathology
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Value of NCSs/EMG
• When neuromuscular disease is present, electrodiagnostic testing can:
• Clarify the type of pathology (i.e. AHC, root, neuropathy, NMJ, or myopathy)
• Determine severity & extent of pathology • Confirm site of pathology • Estimate chronicity of pathology
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Disorders Diagnosed/Evaluated by NCSs/EMG
• Generalized Neuropathies • Axonal (Many etiologies) • Demyelinating
– Acquired » Acute: GBS » Chronic: CIDP
– Hereditary • Mixed
– Diabetic sensorimotor neuropathy – Uremic neuropathy
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Polyneuropathies Continued
• Polyneuropathies associated with many medical conditions
• Multiple investigations often needed • NCSs/EMGs: best initial test to clarify
underlying pathophysiology (i.e., axonal vs demyelination)
• Results may help focus rest of work-up
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Disorders Diagnosed/Evaluated by NCSs/EMG
• Focal Neuropathies – Carpal Tunnel Syndrome (median
neuropathy at the wrist) – Ulnar Neuropathy – Peroneal Nerve Palsy – Others: brachial plexus lesions, tarsal
tunnel syndrome, etc.
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Disorders Diagnosed/Evaluated by NCSs/EMG
• Radiculopathy – Cervical – Lumbar
• Motor Neuron Disease – Amyotrophic lateral sclerosis (ALS) – Spinal muscular atrophy (SMA)
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Disorders Diagnosed/Evaluated by NCSs/EMG
• Muscle Disease – Inflammatory
• Polymyositis, Dermatomyositis – Metabolic – Hereditary or Congenital
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Disorders Diagnosed/Evaluated by NCSs/EMG
• Neuromuscular Junction Disease – Myasthenia Gravis – Lambert Eaton Myasthenic Syndrome – Botulism – Medications
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Nerve Conduction Studies (NCSs) Technical Information
• Peripheral nerves are stimulated with an controlled electrical stimulus
• Responses recorded – Compound motor action potential (CMAP) – Sensory nerve action potential (SNAP) – F wave – H- reflex
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Nerve Conduction Studies
• Motor Latency – Measure of conduction time from nerve segment through
neuromuscular junction to muscle fibers
• Sensory Latency – Measure of conduction time of action potential across a nerve
segment
• Conduction Velocity – Measure of the velocity of the fastest conducting axons
• Motor Amplitude – Measure of the number of activated axons and muscle fibers
• Sensory Amplitude – Measure of the number of activated axons
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Nerve Conduction: Late Responses
• F Wave Latency – Retrograde “rebound” motor impulse – Travels full length of motor axon and back – Information about proximal segments – Limited sensitivity/specificity
• H Reflex – Afferent Path: Sensory axons (group Ia fibers) – Efferent Path: Motor Axons (alpha motor neurons) – Follows muscle stretch reflex arc – Side to side latency most valuable
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Normal Median Motor Study
DL CV Amp (msec) (m/s) (mV) Wrist-APB 3.2 15.0 Elbow-Wrist 55 14.8
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Types of nerve conduction studies
• Sensory: typically antidromic
• Typical nerves examined: Sural, ulnar, median, occasionally superficial radial, superficial peroneal
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Sensory NCS Parameters
• Onset and peak latencies • Conduction velocity
– determined by velocity of a few fast fibers • Amplitude
– determined by the number of large sensory fibers activated
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Normal Median Sensory Study
1 msec/div
Latency CV Amp (msec) (m/s) (uV) Wrist-D2 2.2 58 44.1
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F Waves
• Useful to assess proximal nerve conduction
• Helpful in the evaluation of: – Radiculopathy – Guillian-Barre Syndrome – Peripheral neuropathy – Other demyelinating neuropathies
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F Waves: Normal Median
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H Reflexes
• Useful to assess proximal nerve conduction
• Helpful in the evaluation of: – Polyneuropathy – S1 radiculopathy – Upper Motor Neuron lesions
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F-waves and H-reflex
• Useful for identifying proximal segmental demyelination
• Can only be done when motor amplitude is > 1 mV
• Height-dependent
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Neuromuscular Junction Testing
• Repetitive Nerve Stimulation – Stimulate nerve with train of supramaximal
stimuli before and after exercise – Record from muscle – Attention to technical factors important – More sensitive recording from proximal
muscles
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Repetitive Nerve Stimulation: Normal
3Hz stimulation
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Myasthenia Gravis Repetitive Nerve Stimulation
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Repetitive Nerve Stimulation Myasthenia Gravis
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Single Fiber EMG Model of Potential Pairs
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Limitations of NCSs/EMG
• Generally not helpful in the evaluation/diagnosis of: – Pain from joint disease – Fibromyalgia or myofascial pain syndromes – Central nervous system disorders – Disorders that do not arise from the
neuromuscular system
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What to Expect From an EMG Report
• The reason for the referral is addressed • A clinically and physiologically relevant
interpretation/diagnosis • An outline of the localization, severity, and
acuity of the process • Notation of other diagnoses that are
detected/excluded • Explanation of any technical problems
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What to Expect From an EMG Report
• Data obtained during the study: (NCS) – Amplitude – Distal latency – Distance – Conduction velocity – Normal (Reference) data – Side-to-side comparison (when appropriate) – Limb temperature during the study
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What to Expect From an EMG Report
• Data obtained during the study: (EMG) – Presence & type of abnormal spontaneous
activity – Motor unit recruitment – Motor unit morphology
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EMG “Pearls”
• Electrodiagnostic studies are a supplement to, and not a replacement, for the history and physical examination
• Electrodiagnostic results are often time-dependent
• Electrodiagnostic studies are not “standardized” investigations and may be modified by the practitioner to answer the diagnostic question
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Pitfalls of nerve conduction studies
• Temperature effect and cold limb • Sloppy measurement of distances • Anatomic abnormalities of patient • Technical factors: edema, large limbs, long limbs • Too few nerve conduction studies, lack of
comparisons • Too many nerve conduction studies:
Interpretation of non-existing abnormality