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Complex Regional Pain Syndrome Type 1 — SCE Neurology MCQ

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HardClinical NeurophysiologyComplex Regional Pain Syndrome Type 1SCE Neurology

A 22-year-old has since childhood developed symmetric episodes of burning red hot feet precipitated by warmth and exercise and relieved by cooling. Nerve-conduction studies and skin-biopsy fibre density are normal; her father is similarly affected. Which molecular mechanism is most likely?

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Correct answer: E — Gain-of-function SCN9A variant increasing NaV1.7 excitability

Explanation lettering: D = shown as A · A = shown as C · E = shown as D · C = shown as E

A causes congenital insensitivity to pain rather than heat-triggered burning. B usually causes late-onset sensory ataxia, vestibular areflexia and cough. C is correct: inherited erythromelalgia is a painful channelopathy caused by gain-of-function SCN9A variants affecting NaV1.7; structural fibre tests may be normal. D causes CMT1A with abnormal conduction. E usually presents later with progressive neuropathy and systemic features.

Reference: Small-fibre neuropathy and painful channelopathy: https://pn.bmj.com/content/14/6/368