Calcium and Parathyroid USMLE Step 1 Practice Question
A 52-year-old woman presents with fatigue, polyuria, and polydipsia. Vital signs show BP 138/88, HR 92, RR 16, temp 37.2°C, SpO2 98%. Laboratory studies reveal serum calcium 11.8 mg/dL, phosphate 2.1 mg/dL, PTH 8 pg/mL, and 25-OH vitamin D 45 ng/mL. Urinary calcium is elevated at 320 mg/24h. Imaging shows a solitary 1.2 cm nodule in the right inferior parathyroid gland. Chest X-ray shows no hilar lymphadenopathy. Which of the following best explains her hypercalcemia?
Answer choices
- APTH-secreting parathyroid adenomaCorrect answer
- BVitamin D intoxication from supplements
- CTertiary hyperparathyroidism from chronic kidney disease
- DGranulomatous disease with extrarenal 1,25-dihydroxyvitamin D production
- EThyroid carcinoma with PTHrP secretion
- FMetastatic bone disease with osteoclast-activating cytokine production
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