Development of Hypercalcemia in a Patient Receiving Peginterferon alfa-2a Therapy for Polycythemia Vera.

Peginterferon alfa-2a (PEG-IFN alfa-2a) is commonly used to treat hepatitis C virus infection and is also being used increasingly to treat myeloproliferative neoplasms including polycythemia vera. Sarcoidosis associated with interferon therapy for treatment of hepatitis C is well described, with hypercalcemia occurring as a rare manifestation. We describe a 25-year-old man with polycythemia vera who became resistant to hydroxyurea after 6 years of treatment, requiring therapeutic phlebotomy procedures with increasing frequency for increased hemoglobin and hematocrit levels. PEG-IFN alfa-2a was then initiated at 90 mcg subcutaneously weekly and was progressively increased to 180 mcg weekly over the next 11 months, with normalization of his hemoglobin and hematocrit. The patient then developed hypercalcemia with low parathyroid hormone, parathyroid hormone-related protein, and 25-hydroxy vitamin D levels, and high 1,25-dihydroxyvitamin D and angiotensin-converting enzyme levels, without other evidence of sarcoidosis. PEG-IFN alfa-2a was discontinued, treatment with intravenous fluids and zoledronic acid was initiated, and the hypercalcemia resolved 10 weeks later. Use of the Naranjo Adverse Drug Reaction Probability Scale indicated a probable relationship (score of 7) between the patient's development of hypercalcemia and PEG-IFN alfa-2a therapy; the relationship could not be considered as definite because the patient was not rechallenged with the drug. To our knowledge, this is the first case report of interferon-induced hypercalcemia without other manifestations of sarcoidosis. Practitioners should be aware of hypercalcemia, as well as its protracted time course, as a potential complication of PEG-IFN alfa-2a therapy in patients with myeloproliferative neoplasms. This article is protected by copyright. All rights reserved.