Which indirect cholinergic agonist is used to diagnose myasthenia gravis?

• A. Edrophonium
• B. Xylazine
• C. Guaifenesin
• D. Aminopentamide

Answer: (A)

Indirect cholinergic agonists work by inhibiting acetylcholinesterase, which raises acetylcholine levels at the neuromuscular junction. In myasthenia gravis, where fewer functional acetylcholine receptors are available, boosting acetylcholine can temporarily improve muscle strength. This short-acting effect forms the basis of the diagnostic Tensilon test, using edrophonium. Edrophonium rapidly inhibits acetylcholinesterase, producing a quick and temporary rise in ACh that leads to a noticeable, short-lived improvement in weakness in MG patients. This immediate response is what confirms the diagnosis. The other agents listed do not inhibit acetylcholinesterase and thus are not used for this diagnostic purpose: they lack the mechanism needed to transiently enhance neuromuscular transmission in MG.