Calcium and Parathyroid USMLE Step 1 Practice Question
A 68-year-old woman with a history of non-small cell lung cancer presents to the emergency department with a 3-week history of progressive confusion, polyuria, polydipsia, and constipation. She reports weight loss of 8 pounds over the past month. Vital signs: BP 148/92 mmHg, HR 96 bpm, RR 18, temp 37.1°C. Physical examination reveals dry mucous membranes. Laboratory studies show: serum calcium 12.8 mg/dL (corrected), serum phosphate 2.3 mg/dL, serum creatinine 1.4 mg/dL (baseline 0.9), PTH 18 mIU/L (normal 15-65), 1,25-dihydroxyvitamin D 28 pg/mL (normal 19-67). Chest imaging shows no change in tumor burden. Which of the following is the most likely cause of her hypercalcemia?
Answer choices
- APrimary hyperparathyroidism with concurrent malignancy
- BOsteolytic bone metastases with local PTH-independent calcium mobilization
- CHumoral hypercalcemia of malignancy mediated by parathyroid hormone-related peptide (PTHrP)Correct answer
- DCalcitriol production by granulomatous transformation of malignant cells
- EThyroid hormone-induced osteoclastic bone resorption from paraneoplastic thyroiditis
- FTertiary hyperparathyroidism from chronic kidney disease with secondary hyperparathyroidism
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