A 25-year-old patient develops ascending weakness 3 weeks after Campylobacter jejuni diarrhoea. NCS shows markedly reduced CMAP amplitudes, near-normal sensory responses, and absent F-waves. Anti-GM1 antibodies are strongly positive. Which GBS subtype does this represent?

• A Acute inflammatory demyelinating polyneuropathy (AIDP)
• B Acute motor and sensory axonal neuropathy (AMSAN)
• C Miller Fisher syndrome (MFS)
• D Acute motor axonal neuropathy (AMAN) ✓

Explanation

AMAN (acute motor axonal neuropathy) is characterised by pure motor involvement, reduced/absent CMAPs with preserved sensory nerve action potentials, and association with anti-GM1 (and anti-GD1a) antibodies. It follows Campylobacter jejuni infection most commonly and is predominant in Asian and Latin American countries. The molecular mimicry between C. jejuni lipopolysaccharide and gangliosides drives antibody-mediated attack on motor axons at the nodes of Ranvier. AIDP shows demyelinating pattern (prolonged latencies, dispersed CMAPs, reduced conduction velocity). AMSAN involves both motor and sensory axons. MFS features ophthalmoplegia, ataxia, areflexia with anti-GQ1b antibodies.

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

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Written and medically reviewed by the StethoPrep medical team.