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ABPN Neuromuscular Medicine study materials
ABPN Neuromuscular Medicine study resources

ABPN Neuromuscular Medicine: Neuromuscular Medicine: Core Localization and Diagnostic Reasoning

ABPN Neuromuscular Medicine · Work through your exam, one topic at a time.

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Neuromuscular Medicine: Core Localization and Diagnostic Reasoning

Start with localization, not with the test

Every neuromuscular question rewards a disciplined anatomic approach. Decide first whether the lesion is anterior horn cell, root/plexus, peripheral nerve, neuromuscular junction (NMJ), or muscle. Patterns that point to muscle: symmetric proximal weakness, normal sensation, normal reflexes until late. Patterns that point to nerve: weakness respecting a nerve or root territory, sensory loss, early reflex loss. NMJ disease gives fatigable weakness with preserved sensation and reflexes.

The concepts to own

  • Upper vs lower motor neuron signs: atrophy, fasciculations, and hyporeflexia are LMN; spasticity, hyperreflexia, and Babinski are UMN. ALS uniquely combines both, with sensory sparing and no sphincter involvement.
  • Temporal profile: acute (hours-days: Guillain-Barre, vasculitis, toxin), subacute (weeks: inflammatory myopathy, CIDP), chronic (months-years: inherited neuropathies, dystrophies).
  • NCS/EMG logic: demyelination = slowed conduction velocity, prolonged distal latency, conduction block, temporal dispersion; axonal loss = reduced amplitudes. Myopathy = short-duration, low-amplitude MUAPs with early recruitment; neuropathic = large, long-duration MUAPs with reduced recruitment. Fibrillations signal active denervation.
  • CSF and antibody testing are chosen to confirm a localization already suspected clinically.

Traps examiners use

  1. Calling a myasthenic patient "weak" without noting fatigability or the sensory-sparing pattern.
  2. Confusing conduction block (demyelinating) with axonal loss on EMG.
  3. Missing autonomic or bulbar features that reclassify the diagnosis.
  4. Assuming normal reflexes exclude NMJ disease; they are typically normal or increased.

Rule of thumb

If weakness is proximal and symmetric with normal sensation and reflexes, think muscle or NMJ; if it follows a nerve distribution with sensory loss and areflexia, think peripheral nerve; if it mixes UMN and LMN signs without sensory loss, think ALS.