I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
Q- A previously healthy 52-year-old woman comes to the physician because of a 2-month history of fatigue, constipation, and frequent urination. Her temperature is 37.1°C (98.8°F), pulse is 80/min, respirations are 14/min, and blood pressure is 140/90 mm Hg. Diffuse crackles are heard bilaterally. Her serum calcium concentration is 11.1 mg/dL, and serum parathyroid hormone concentration is decreased. A chest x-ray shows bilateral hilar lymphadenopathy and interstitial infiltrates. Which of the following is the most likely cause of this patient’s hypercalcemia?
(A) Calcitriol production by activated macrophages
(B) Local resorption of bone by metastases
(C) Parathyroid hormone-related peptide secretion
(D) Secretion of parathyroid hormone
(E) Secretion of thyroid-stimulating hormone
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Answer
Hypercalcemia with decreased PTH indicate non-parathyroid-related hypercalcemia, ruling out options (D) and (E). Common causes of hypercalcemia include malignancy, granulomatous diseases, and excessive vitamin D intake. Bilateral hilar lymphadenopathy and interstitial infiltration suggest a granulomatous disease such as sarcoidosis which contains activated macrophages that produce calcitriol (1,25-dihydroxyvitamin D), leading to increased intestinal calcium absorption.
The correct answer is A