Tumor-induced hypophosphatemic osteomalacia diagnosed by the combinatory procedures of magnetic resonance imaging and venous sampling for FGF23.

This report describes a 37-year-old man with tumor-induced osteomalacia (TIO). The patient had hypophosphatemia and elevated fibroblast growth factor 23 (FGF23) in the peripheral blood. Magnetic resonance imaging detected an abnormal mass in the left greater trochanter. Venous sampling revealed a significantly higher level of FGF23 in the left common iliac vein (proximal to the tumor), verifying that the tumor is responsible for TIO. The serum level of FGF23 decreased and symptoms improved after removal of the tumor. The combined diagnostic procedures of MRI and venous sampling for FGF23 effectively detected the tumor responsible for TIO.