INHIBITION OF 1,25(OH)2D PRODUCTION BY HYPERCALCEMIA IN OSTEITIS-FIBROSA CYSTICA - INFLUENCE ON PARATHYROID-HORMONE SECRETION AND HUNGRY BONE-DISEASE

Primary hyperparathyroidism is usually associated with normal or eleva ted serum 1,25-dihydroxyvitamin D [1,25(OH)2D] levels. We report a 63- year-old patient with extreme hypercalcemia (ionized serum calcium, 2. 51 mmol/l; normal range, 1.19-1.36), very high serum concentrations of intact immunoreactive parathyroid hormone (iPTH) (145 pmol/l; normal range, 1-6.8), radiological lesions of osteitis fibrosa cystica, only mildly impaired renal function (creatinine clearance, 69 ml/min/M2) an d very low serum levels of 1,25(OH)2D (28.8 pmol/l; normal range, 72-1 20). Presurgery normalization of the calcemia with normal saline, salm on calcitonin and pamidronate caused an increase in 1,25(OH)2D serum c oncentration to 228.3 pmol/l. A negative correlation could be establis hed between ionized calcium and 1,25(OH)2D levels during that period ( r2=0.80, P < 0.04). While serum calcium decreased with treatment, seru m iPTH also decreased to 48.6 pmol/l, suggesting some 1,25(OH)2D inhib ition of parathyroid adenoma function. Serum alkaline phosphatase also rose from 309 to 390 units/l (normal range, 25-97), suggesting the be ginning of resolution of her osteitis fibrosa cystica prior to surgery . Surgical removal of a parathyroid adenoma was associated with a decr ease in serum calcium and iPTH levels. To our surprise, the hypocalcem ia could be managed easily with 1500 mg of oral calcium carbonate dail y, even if the hungry bone disease became more active with an increase in alkaline phosphatase to 486 units/l. This was explained by the ver y high levels of serum 1,25(OH)2D (>200 pmol/l) which prevailed in the postsurgery period and were probably related to decreased bone resorp tion and increased bone formation. This case illustrates that normaliz ing serum calcium prior to surgery in patients with primary hyperparat hyroidism and osteitis fibrosa cystica can be highly beneficial.