Calcium and Parathyroid USMLE Step 1 Practice Question
A 61-year-old woman presents with progressive fatigue, constipation, and diffuse bone pain for 3 months. Vital signs: BP 138/88, HR 92, RR 16, Temp 37°C, SpO2 98%. Hand radiographs demonstrate subperiosteal bone resorption. Laboratory studies reveal serum calcium 11.2 mg/dL (normal 8.5–10.2), PTH 187 pg/mL (normal 15–65), and normal 25-hydroxyvitamin D level. She denies recent weight loss. Which pathophysiologic mechanism best explains her skeletal findings?
Answer choices
- AParathyroid hormone induced osteoblast expression of RANKLCorrect answer
- BInhibition of renal 1 alpha hydroxylase by parathyroid hormone
- CDecreased osteoblast activity from low thyroid hormone
- DDirect osteoclast stimulation by parathyroid hormone
- ECalcitonin mediated activation of osteoclasts
- FDecreased osteoprotegerin production by osteoblasts due to elevated parathyroid hormone
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