Osteoporosis associated with aging is considered the most common cause of bone mineral loss. Osteomalacia, abnormal bone loss with excess osteoid formation, is another cause. A 46-year-old man was examined for chronic hip and lower extremity pain that had not been relieved by nonsteroidal anti-inflammatory drugs or steroids. A bone scan revealed multiple foci of activity. The serum calcium level was normal, but phosphorus values were low. These results did not correspond with the indications for typical hyperparathyroid disease, so another cause was sought. An In-111 octreotide scan showed a focus in the right humeral head. At surgery, a phosphaturic tumor of mesenchymal origin was partially resected. Oncogenic osteomalacia is related to secretion of a phosphaturic material from a fibroblast growth factor.
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