Severe hypophosphatemia in a 79-year-old man.

A 79-year-old white man with a history of progressive bone pain was admitted for evaluation 3 years ago. The patient reported that the pain began in both feet and gradually spread to the rest of the body over a 2-year period. Further assessment revealed multiple stress fractures in the feet. Bone mineral density test indicated osteopenia. Serial bone mineral density tests during the 2 years showed that his osteopenia was progressing. Results of several serum protein electrophoreses were essentially normal. His medical history, which included surgical removal of a cerebral aneurysm near the sella turcica and bacterial meningitis, suggested no pertinent etiologic factors. Physical examination revealed no clinically significant findings except unsteady gait. His serum phosphate concentrations declined from 2.5 to 1.8 mg/dL over the 2 years before admission. Laboratory test results at the time of admission are summarized in Table 1. The patient’s phosphate concentration reached a nadir of 1.2 mg/dL at admission. His serum alkaline phosphatase was increased. Other notable abnormalities included low normal calcium, normal to borderline high parathyroid hormone (PTH), 2 and increased 24-h urine phosphate and calcium excretion. Other routine biochemical parameters [including ionized calcium, thyroid-stimulating hormone, and free thyroxine (T4)] were normal. The patient underwent a whole-body scan showing multiple bone lesions. Diagnostic imaging studies including x-ray, a computer axial tomography (CAT), and MRI of the lungs, abdomen, and pelvis were reported to be normal at admission.