Tumor-induced osteomalacia: the importance of measuring serum phosphorus levels.

BACKGROUND: A previously healthy 32-year-old man presented with pain in his chest, ankle, and hip. His musculoskeletal pain progressed over the course of 6 months to the point of difficulty with ambulation. INVESTIGATIONS: Radiographic studies included chest and ankle X-rays, multiple bone scans, and foot and pelvic MRI. Laboratory evaluation comprised a serum chemistry panel (including electrolyte levels, renal function tests and liver function tests), and measuring serum levels of phosphorus, parathyroid hormone, vitamin D, alkaline phosphatase, and fibroblast growth factor 23, as well as urine levels of calcium and phosphorus. DIAGNOSIS: Tumor-induced osteomalacia. MANAGEMENT: The patient received phosphate and vitamin D supplementation in the form of potassium-phosphorus (500 mg, three times daily) and calcitriol (0.5 microg, three times daily). Six months after his first presentation, he underwent surgical resection of a rib mass, with subsequent normalization of phosphorus concentration.