Hypercalcemia occurs in 10 to 30% of renal transplant recipients and is most often due to persistent hyperparathyroidism. Herein we describe a patient with a history of hyperparathyroidism who sought medical assessment because of recurrence of hypercalcemia 7 years after a successful renal transplantation. The hypercalcemia was associated with a normal serum phosphate level, a low to normal parathyroid hormone level, virtually undetectable levels of parathyroid hormone-related protein, and increased 1,25-dihydroxyvitamin D levels. Further assessment led to the diagnosis of an underlying lymphoma. To our knowledge, this is the first report of 1,25- dihydroxyvitamin D-mediated hypercalcemia in a renal transplant recipient with lymphoma. The possibility of an underlying lymphoproliferative disorder should be considered in the differential diagnosis of hypercalcemia in a renal transplant recipient.
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