A 35-year-old woman develops rapidly progressive ascending weakness over 3 days following a respiratory tract infection. She has areflexia and cannot walk unaided. CSF shows albumino-cytological dissociation (protein 280 mg/dL, cells 4/μL). Nerve conduction studies show prolonged distal latencies and reduced conduction velocities. Which is the MOST specific electrodiagnostic finding distinguishing acute inflammatory demyelinating polyneuropathy (AIDP) from acute motor axonal neuropathy (AMAN)?
- A Areflexia and ascending paralysis pattern
- B Prolonged F-wave latencies
- C Reduced conduction velocity and prolonged distal latencies (demyelinating pattern) ✓
- D Albuminocytological dissociation in CSF
Correct answer: C. Reduced conduction velocity and prolonged distal latencies (demyelinating pattern)
Explanation
AIDP (the classic demyelinating form of GBS) shows reduced nerve conduction velocities, prolonged distal latencies, conduction block, and temporal dispersion on NCS — all hallmarks of demyelination. AMAN (axonal variant) shows normal or near-normal conduction velocities with reduced CMAP amplitudes — indicating axonal damage with preserved myelin. CSF albuminocytological dissociation and clinical features are common to all GBS variants. Anti-GM1 and anti-GD1a antibodies are more specific for AMAN.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.