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AIDP vs CIDP – Diagnostic Distinction — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularAIDP vs CIDP – Diagnostic DistinctionSCE Neurology

A 50-year-old man presents with a 4-week history of progressive difficulty walking. He has bilateral leg weakness and paresthesiae ascending to the waist, with bladder dysfunction. He has areflexia in the legs but upper limb reflexes are normal. NCS show markedly prolonged distal motor latencies and very slow motor conduction velocities (<20 m/s) in the lower limbs. CSF protein is 2.5 g/L with 3 cells/µL. Symptoms have been progressing slowly over 4 weeks. What is the most important diagnostic distinction to make?

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Correct answer: A — AIDP vs CIDP — determine whether this is acute (<4 weeks) or chronic (>8 weeks) inflammatory demyelinating polyneuropathy

This patient has a subacute (4-week) demyelinating polyneuropathy. The critical clinical question is whether this represents AIDP (GBS) that is still evolving (symptoms typically plateau by 4 weeks) or CIDP that is still in its early course (defined as progression beyond 8 weeks). The distinction matters because CIDP requires long-term immunomodulatory therapy whereas GBS is treated with IVIg/PLEX acutely. If symptoms continue to progress beyond 8 weeks, the diagnosis shifts to CIDP. B: Upper limb preservation with areflexia and NCS findings argue against myelitis. C: NCS clearly show neuropathy. D: The acute/subacute onset suggests acquired. E: Large fibre involvement is evident from NCS.

Reference: EAN/PNS CIDP Guidelines (2021); EAN/PNS GBS Guidelines (2023)