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Myasthenia gravis — USMLE Step 2 CK MCQ

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ModerateInternal MedicineMyasthenia gravisUSMLE Step 2 CK

A 43-year-old African American man comes to the clinic because of progressive symptoms. History and focused examination are notable for fluctuating ptosis and diplopia that worsen with use. Temperature is 98.6°F (37.0°C), blood pressure is 126/78 mmHg, pulse is 84/min, respirations are 16/min, and oxygen saturation is 98% on room air. Physical examination confirms the key finding and shows no unrelated abnormality that would better explain the presentation. Focused laboratory studies and initial testing support the clinical pattern described in the stem. Which of the following is the most appropriate initial diagnostic study?

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Correct answer: C — Acetylcholine receptor antibody testing

The vignette describes Myasthenia gravis, supported by fluctuating ptosis and diplopia that worsen with use. Acetylcholine receptor antibody testing is the single best answer because it matches the diagnostic or management priority in this clinical setting. The other choices are plausible alternatives in related presentations, but they do not best fit the timing, findings, and guideline-directed approach described here.

Reference: https://www.ncbi.nlm.nih.gov/books/#stage-9-order-21