Parathyroid hormone-related protein: an unusual mechanism for hypercalcemia in sarcoidosis

Abstract

Objective: To describe parathyroid hormone-related protein (PTHrP) as a mediator of hypercalcemia in sarcoidosis.

Methods: We present a detailed case report including history, physical, laboratory testing, pathology findings, and follow-up data over 2 years. We also propose a possible mechanism for PTHrP-mediated hypercalcemia in sarcoidosis.

Results: A 56-year-old man presented with abdominal pain, fatigue, and excess thirst. Routine laboratory testing demonstrated severe hypercalcemia. The patient was admitted for treatment and work-up. Inpatient work-up was significant for suppressed parathyroid hormone, low 25-hydroxyvitamin D, normal 1,25-dihydroxyvitamin D, and elevated PTHrP. The patient was treated for hypercalcemia and discharged for follow-up. Malignancy screening included computed tomography of the chest, which revealed parenchymal nodules and diffuse lymphadenopathy. Biopsy revealed nonnecrotizing granulomatous inflammation with positive PTHrP staining by immunohistochemistry. After treatment with intravenous hydration and glucocorticoids, the hypercalcemia resolved and on subsequent follow-up, PTHrP levels had normalized to 0.5 pmol/L.

Conclusion: PTHrP may be a possible mediator of hypercalcemia in sarcoidosis. The differential diagnosis of PTHrP-induced hypercalcemia should include sarcoidosis, and further research is needed to establish the incidence and source of PTHrP in sarcoidosis.