Electrolyte Disorders USMLE Step 1 Practice Question
A 41-year-old woman presents with a 2-year history of recurrent kidney stones and persistent hypercalciuria. She denies taking vitamin supplements or medications. Physical examination reveals bilateral hilar lymphadenopathy and erythema nodosum on her shins. Laboratory studies show: serum calcium 9.8 mg/dL (normal 8.5-10.5), serum phosphate 2.1 mg/dL (normal 2.5-4.5), PTH 15 pg/mL (normal 15-65), and 1,25-dihydroxyvitamin D 68 pg/mL (normal 24-86). Twenty-four-hour urine calcium is elevated at 480 mg/day (normal <300). Which of the following is the most likely diagnosis?
Answer choices
- APrimary hyperparathyroidism with secondary nephrolithiasis
- BVitamin D intoxication from surreptitious supplement use
- CFamilial hypophosphatemic rickets (X-linked hypophosphatemia)
- DSarcoidosis with extrarenal 1,25-dihydroxyvitamin D productionCorrect answer
- EHyperthyroidism with increased bone turnover
- FLymphoma with paraneoplastic calcitriol secretion
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