Studies in a patient with tumor-induced hypophosphatemic osteomalacia.

A 7-year study of a patient with tumor (hemangiopericytoma)-induced hypophosphatemic osteomalacia (TIO) is presented, and the findings are in keeping with the depressed tubular reabsorption of phosphate and low 1,25(OH)2 vitamin D levels seen in other studies. Despite normalization of 1,25(OH)2 vitamin D levels with pharmacologic doses of vitamin D2, there was no discernible effect on serum phosphorus levels. Also, despite hypercalcemia induced by pharmacologic doses of vitamin D2, serum parathyroid hormone levels were persistently elevated, and gradually returned to subnormal levels after removal of the tumor. Following removal of the tumor, there was a rapid increase of the 1,25(OH)2 vitamin D levels to supraphysiologic levels, prompt appropriate increase in tubular reabsorption of phosphate levels, and symptomatic improvement in the osteomalacia. Speculations on the physiologic and pathophysiologic role of the putative hormone(s) produced by the tumors associated with this syndrome are presented.