In Guillain-Barré syndrome, which electrodiagnostic finding on nerve conduction studies suggests the acute motor axonal neuropathy (AMAN) subtype rather than the classic acute inflammatory demyelinating polyradiculoneuropathy (AIDP)?

• A Prolonged distal latencies, slowed conduction velocity, and F-wave absence
• B Conduction block with normal distal CMAP amplitude
• C Absent SNAPs with normal CMAPs
• D Low CMAP amplitude with preserved conduction velocity and normal F-wave latency in the acute phase ✓

Explanation

AMAN (acute motor axonal neuropathy) is characterised by isolated motor involvement with low or absent CMAP amplitudes but preserved or only mildly slowed conduction velocities (reflecting primary axonal rather than myelin pathology). F-wave latencies may be normal in early stages. AIDP (classic GBS) shows demyelinating features: prolonged distal latencies, reduced conduction velocities, prolonged or absent F-waves, and conduction block. Absent SNAPs with normal CMAPs suggest AMSN (acute motor-sensory axonal neuropathy) or dorsal root ganglion involvement.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.