Calcium and Parathyroid USMLE Step 1 Practice Question
A 35-year-old woman presents 2 days after thyroidectomy with perioral tingling, hand cramps, and episodes of facial muscle twitching. Vital signs: BP 118/76, HR 92, RR 16, Temp 37.2°C, SpO2 98% on room air. Laboratory studies show serum calcium 7.2 mg/dL (normal 8.5–10.5), phosphate 4.8 mg/dL. She denies dyspnea or chest pain. Which of the following best explains why low serum calcium produces these neuromuscular symptoms?
Answer choices
- ADecreased threshold for opening of neuronal sodium channelsCorrect answer
- BEnhanced muscarinic receptor blockade
- CSuppression of acetylcholine release at the neuromuscular junction
- DIncreased threshold for opening of neuronal sodium channels
- EReduced myelin synthesis in peripheral nerves
- FIncreased permeability of the blood-brain barrier to excitatory neurotransmitters
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