Plasma-cell granuloma producing calcitriol and hypercalcemia.

A teenage boy presented with hypercalcemia and a large intrathoracic mass. Results of an extensive evaluation, including normal findings on parathyroid hormone and urinary 3', 5'-cyclic adenosine monophosphate assays, failed to explain his hypercalcemia. During surgery, a large plasma-cell granuloma of the right middle and lower lobes was resected. Within 2 weeks, serum calcium levels returned to normal. Serum calcitriol (1,25-dihydroxyvitamin D3) levels were elevated before surgery and decreased to normal afterward, correlating with the serum calcium level. Homogenates of the plasma-cell granuloma synthesized a compound indistinguishable from calcitriol.