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Sarcoidosis with hypercalcemia — RCPSC IM MCQ

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HardRespirologySarcoidosis with hypercalcemiaRCPSC IM

A 38-year-old has erythema nodosum, ankle arthritis, bilateral hilar lymphadenopathy, calcium 2.92 mmol/L and suppressed parathyroid hormone. Which mechanism best explains the hypercalcemia?

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Correct answer: D — Unregulated extrarenal calcitriol production by activated granuloma macrophages

The best answer is “Unregulated extrarenal calcitriol production by activated granuloma macrophages”. Sarcoid granuloma macrophages express 1-alpha-hydroxylase outside normal renal feedback, increasing calcitriol and intestinal calcium absorption while suppressing PTH. The clinical triad supports sarcoidosis rather than parathyroid, humoral malignant or osteolytic mechanisms. Suppressed parathyroid hormone makes primary hyperparathyroidism unlikely, while the sarcoid phenotype and absence of a cancer syndrome argue against parathyroid-hormone-related peptide or osteolytic disease.

Reference: Canadian Thoracic Society, guideline library: https://cts-sct.ca/guideline-library/