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Neuromuscular blocker response in myasthenia gravis — FRCA Primary MCQ

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HardPharmacologyNeuromuscular blocker response in myasthenia gravisFRCA Primary

A patient with myasthenia gravis requires emergency laparotomy. A small dose of non-depolarising neuromuscular blocker causes profound weakness, but suxamethonium has a reduced initial effect. What best explains this pattern?

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Correct answer: B — Upregulation of extrajunctional acetylcholine receptors

Myasthenia gravis reduces functional postsynaptic nicotinic receptors, increasing sensitivity to non-depolarising blockers and reducing response to depolarising suxamethonium. Extrajunctional receptor upregulation is more relevant after burns, denervation and prolonged immobility. Plasma cholinesterase activity does not explain the receptor-level pattern. The pearl is that quantitative monitoring and dose reduction are essential.

Reference: RCoA Primary FRCA Syllabus 2026; Peck, Hill & Williams Pharmacology for Anaesthesia