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Edrophonium Test – Mechanism — SCE Neurology MCQ

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EasyPeripheral Neuropathy & NeuromuscularEdrophonium Test – MechanismSCE Neurology

A 55-year-old woman with myasthenia gravis presents with worsening weakness. Her neurologist performs an edrophonium (Tensilon) test. After IV administration of edrophonium, her ptosis transiently improves for 3–4 minutes. What is the mechanism of this test?

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Correct answer: D — Edrophonium is a short-acting acetylcholinesterase inhibitor that transiently increases acetylcholine at the neuromuscular junction

Edrophonium (Tensilon) is an ultra-short-acting acetylcholinesterase inhibitor (duration 3–5 minutes). By inhibiting acetylcholine breakdown at the NMJ, it transiently increases ACh concentration, improving neuromuscular transmission. A positive test (improvement in weakness) supports MG but is not specific — false positives occur. The test is now rarely performed due to cardiac risks (bradycardia, asystole) and availability of serological testing. Atropine must be available as an antidote. A: Edrophonium does not affect dopamine. C: It does not directly agonise nicotinic receptors. D: It does not block antibodies. E: It does not affect calcium channels.

Reference: ABN MG Guidelines (2025)