Neuromuscular Disorders USMLE Step 1 Practice Question
A 36-year-old woman with myasthenia gravis self-increased her pyridostigmine dose without medical supervision. She presents with generalized weakness, diarrhea, diaphoresis, and miosis. Vital signs show BP 128/76, HR 92, RR 18, temperature 37.2°C, and SpO2 98% on room air. Serum potassium is 3.1 mEq/L. She denies recent infections or medication changes besides pyridostigmine. Which mechanism best explains her current clinical deterioration?
Answer choices
- AVoltage gated calcium channel antibodies from lung cancer
- BAcute demyelinating polyneuropathy after infection
- CProgression to ALS with autonomic failure
- DUnder-treatment of myasthenia causing only nicotinic receptor blockade
- EExcess acetylcholine causing depolarization block with muscarinic symptomsCorrect answer
- FAutoimmune destruction of the neuromuscular junction by anti-MuSK antibodies triggered by pyridostigmine
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