USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

In what scenario would an under-treated myasthenia gravis patient show improvement following an edrophonium infusion?

1. No response to edrophonium

2. Exacerbation of symptoms

3. Immediate symptom relief

4. Symptom improvement indicates the need for increased AChE inhibitor dose

The correct answer is: Symptom improvement indicates the need for increased AChE inhibitor dose

In the context of myasthenia gravis, an autoimmune disorder that affects the transmission of nerve impulses to muscles, the use of edrophonium, a short-acting acetylcholinesterase (AChE) inhibitor, can help determine the adequacy of treatment. Edrophonium temporarily increases the amount of acetylcholine available at the neuromuscular junction by inhibiting its breakdown, which can lead to symptom relief in patients who are under-treated. When a patient with myasthenia gravis shows marked improvement in symptoms after an edrophonium infusion, it signifies that the underlying cholinergic deficit is contributing to their muscle weakness, indicating that current therapy with AChE inhibitors is insufficient. This immediate symptom relief strongly suggests that there is potential for further therapeutic gain with increased dosage of AChE inhibitors or alternative treatments. Therefore, the enhancement of muscular strength following the infusion is indicative of the need for adjustment in the patient's medication regimen to optimize treatment and address symptoms effectively.