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Pathology · Inflammation and repair: sarcoidosis hypercalcaemia
Sample itemA 35-year-old woman with bilateral hilar lymphadenopathy and non-caseating granulomas has a serum calcium of 12.5 mg/dL. What is the mechanism of the hypercalcaemia?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
B. Granuloma macrophages convert vitamin D to its active form
Activated macrophages in sarcoid granulomas express 1-alpha hydroxylase, so they make calcitriol independent of calcium and PTH. This increases gut calcium absorption, and PTH is suppressed.
Option by option
A. Autonomous parathyroid secretion
Primary hyperparathyroidism would have high PTH, while sarcoid hypercalcaemia has low PTH.
B. Granuloma macrophages convert vitamin D to its active form (correct)
Correct. Extra-renal 1-alpha hydroxylase in granuloma macrophages raises calcitriol.
C. Osteolysis by metastases
Sarcoid is not metastatic, and bone metastases are not present.
D. Secretion of PTH-related protein by granuloma cells
PTHrP is made by squamous carcinomas and some lymphomas and is not the mechanism in sarcoid.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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