Which agent could be used to diagnose myasthenia gravis in a patient showing symptoms of muscle fatigue and drooping eyelids?

Edrophonium is the correct choice for diagnosing myasthenia gravis due to its mechanism of action as a short-acting acetylcholinesterase inhibitor. In this condition, there is an autoimmune response that leads to the destruction of acetylcholine receptors at the neuromuscular junction, resulting in muscle weakness and fatigue.

When edrophonium is administered, it temporarily increases the levels of acetylcholine at the junction by inhibiting its breakdown. If a patient has myasthenia gravis, they will often show a marked improvement in muscle strength and a reduction in symptoms, such as eyelid drooping, shortly after administration of the drug. This rapid response serves as a diagnostic tool for the condition.

The other agents listed do not serve the same diagnostic purpose. Atropine, for instance, is an anticholinergic agent that would likely worsen the symptoms of myasthenia gravis due to its ability to block acetylcholine receptors. Pralidoxime is primarily used in cases of organophosphate poisoning and not in the diagnosis of neuromuscular disorders. Echothiophate is another acetylcholinesterase inhibitor but is used for the treatment of glaucoma and not for diagnosing myasthen