Neurodegenerative Diseases USMLE Step 1 Practice Question
A 34-year-old woman presents with progressive bilateral ptosis and diplopia that worsen in the evening. She reports difficulty chewing after prolonged meals and denies sensory changes. Vital signs: BP 118/76, HR 82, RR 14, Temp 37°C, SpO2 98%. Neurologic examination confirms fatigable extraocular weakness and bilateral ptosis; reflexes and sensation are intact. Serum acetylcholine receptor antibodies are positive. Which of the following mechanisms best explains this disorder?
Answer choices
- ADemyelination of peripheral nerves after infection
- BMutation in dystrophin causing myofiber necrosis
- CAntibodies against presynaptic P Q type calcium channels
- DDegeneration of dopaminergic neurons in the substantia nigra
- EAntibodies against postsynaptic acetylcholine receptorsCorrect answer
- FMuscle-specific kinase (MuSK) antibodies blocking acetylcholine receptor clustering
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