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Dopa-Responsive Dystonia — SCE Neurology MCQ

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HardMovement DisordersDopa-Responsive DystoniaSCE Neurology

A 34-year-old has lifelong fatigable limb-girdle weakness and intermittent ptosis but no sensory loss. AChR, MuSK and LRP4 antibodies are negative. Single nerve stimuli produce a repetitive compound muscle action potential, and pyridostigmine previously worsened respiratory symptoms. Which molecular diagnosis and treatment pairing is most coherent?

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Correct answer: A — Biallelic COLQ congenital myasthenic syndrome; oral salbutamol

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

A is correct: COLQ deficiency causes endplate acetylcholinesterase deficiency, prolonged acetylcholine action and a repetitive CMAP; acetylcholinesterase inhibitors can worsen it, whereas oral salbutamol or ephedrine may produce substantial benefit. DOK7 disease is usually recessive and may also respond to salbutamol, but high-dose pyridostigmine is not the defining pairing. RAPSN and CHRNE syndromes are genetic rather than antibody-mediated, so plasma exchange and corticosteroids do not correct their mechanism.

Reference: Neuromuscular junction disorders: mimics and chameleons: https://pn.bmj.com/content/24/6/467