Calcium and Parathyroid USMLE Step 1 Practice Question
A 54-year-old man with newly diagnosed pulmonary sarcoidosis presents with fatigue, weakness, and polyuria. Vital signs show BP 138/88 mmHg, HR 92 bpm, RR 18/min, temp 37.2°C, SpO2 98% on room air. Serum calcium is 11.8 mg/dL, phosphate 3.8 mg/dL, PTH 18 mIU/L, and 1,25-dihydroxyvitamin D markedly elevated. Serum creatinine is 1.2 mg/dL with normal urinary calcium. Chest X-ray shows bilateral hilar lymphadenopathy. Which pathophysiologic mechanism best explains these findings?
Answer choices
- AExtrarenal 1-alpha-hydroxylase production by activated macrophages in granulomasCorrect answer
- BPTHrP secretion from sarcoid nodules in the lungs
- CParathyroid hyperplasia from chronic phosphate wasting
- DIncreased intestinal calcium absorption from dietary supplementation
- EImpaired renal 24-hydroxylase activity causing vitamin D accumulation
- FGranulomatous infiltration of the parathyroid glands leading to increased PTH production
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