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Myotonic dystrophy type 1 — SCE Neurology MCQ

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ModerateNeuromuscularMyotonic dystrophy type 1SCE Neurology

A 35-year-old man has difficulty releasing his grip after a handshake, early cataracts and excessive daytime sleepiness. Examination shows temporal wasting, distal weakness and percussion myotonia. ECG shows first-degree atrioventricular block. What is the most likely diagnosis?

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Correct answer: A — Myotonic dystrophy type 1

Myotonic dystrophy type 1 is the best answer. Myotonia with distal weakness, cataracts, facial wasting and conduction disease is classic myotonic dystrophy type 1. Becker dystrophy is proximal; myasthenia causes fatigability not myotonia; thyrotoxic periodic paralysis is episodic; IBM affects older adults with finger flexor/quadriceps weakness. Clinical pearl: Cardiac conduction disease is a major surveillance issue in myotonic dystrophy.

Reference: GeneReviews myotonic dystrophy; BNF