Neuromuscular Disorders USMLE Step 1 Practice Question
A 29-year-old woman comes to the clinic because of double vision and drooping of both eyelids that worsen by the end of the day. She also reports difficulty chewing meat at dinner after being able to eat breakfast normally. Examination shows fatigable ptosis and normal pupillary responses. Which of the following is the most likely underlying mechanism of her disorder?
Answer choices
- ASegmental demyelination of peripheral nerves after infection
- BMutation causing absent dystrophin in skeletal muscle
- CAutoantibodies against postsynaptic nicotinic acetylcholine receptorsCorrect answer
- DAutoantibodies against presynaptic voltage gated calcium channels
- EDegeneration of upper and lower motor neurons
- FLRP4 antibodies blocking agrin-MuSK signaling
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