Tumor-related osteomalacia followed after treatment by hyperparathyroidism.

Tumor-induced osteomalacia is due to renal phosphate wasting in response to a humoral factor produced by a tumor, usually a benign mesenchymal tumor. Removal of the tumor is followed by resolution of the metabolic disorder. Physicians should be aware that sporadic renal phosphate wasting in an adult should prompt a search for a tumor. A case of tumor-induced osteomalacia due to a nonossifying fibroma of the radius is reported. After removal of the tumor, renal phosphate excretion returned to normal, but the patient developed tertiary hyperparathyroidism. Eight years elapsed between symptom onset and the diagnosis of the tumor. The pathogenesis of tumor-induced osteomalacia and the role of treatment for renal phosphate wasting on the subsequent development of hyperthyroidism are discussed.