Question

A 43-year-old woman with diagnosed myasthenia gravis, and taking pyridostigmine daily, presents in the neurology clinic with profound skeletal muscle weakness. You are unsure whether she is experiencing a cholinergic crisis or a myasthenic crisis, so you administer a usually appropriate diagnostic dose of parenteral edrophonium. Assume the patient was actually experiencing a cholinergic crisis. What is the most likely response to the edrophonium?

a. Hypertensive crisis from peripheral vasoconstriction
b. Myocardial ischemia, and angina, from drug-induced tachycardia and coronary vasoconstriction
c. Premature ventricular contractions from increased ventricular automaticity
d. Prompt improvement of skeletal muscle tone and function
e. Ventilatory distress or failure

Answer 1

If a patient with myasthenia gravis is experiencing a cholinergic crisis, administering edrophonium is likely to result in ventilatory distress or failure due to overaccumulation of acetylcholine at the neuromuscular junction.

Step-by-step explanation:

If a 43-year-old woman with a diagnosis of myasthenia gravis and on daily medication with pyridostigmine presents with profound skeletal muscle weakness and it is unclear whether she is experiencing a cholinergic crisis or a myasthenic crisis, administration of edrophonium, which is a rapid-acting acetylcholinesterase inhibitor, could be used to differentiate between the two. However, if she were actually in a cholinergic crisis, the administration of edrophonium would likely exacerbate the symptoms due to the further accumulation of acetylcholine at the neuromuscular junction. The most likely response to the edrophonium would be e. Ventilatory distress or failure, as this is indicative of an excessive cholinergic state, which can overload the already compromised neuromuscular junction and precipitate respiratory muscle weakness and failure.