Tumor-Induced Osteomalacia Localized by Systemic Venous Sampling and ⁶⁸Ga-DOTATOC Positron Emission Tomography

Tumor-induced osteomalacia is characterized by hypophosphatemia and fragility fractures caused by fibroblast growth factor 23 (FGF23)-producing tumors. We report a case of tumor-induced osteomalacia in which the tumor location could be determined by gallium 68 (⁶⁸Ga)-DOTATOC positron emission tomography (PET)/computed tomography (CT). A 74-year-old woman had recurrent fractures and bone pain. Blood tests showed hypophosphatemia and elevated serum alkaline phosphatase and FGF23 levels and CT and bone scintigraphy showed multiple bone fractures. Tumor-induced osteomalacia was therefore suspected. Indium 111 (¹¹¹In)-pentetreotide scintigraphy showed focus of increased activity in the head, and CT and magnetic resonance images showed a mass-like lesion in the posterior ethmoidal sinus. However, in systemic venous sampling, serum FGF23 level was highest in the left common iliac vein. ⁶⁸Ga-DOTATOC PET/CT clearly demonstrated focal uptake in the left anterior inferior iliac spine consistent with systemic venous sampling. Retrospectively analyzed, focal uptake in the head was considered to be a physiological uptake in the pituitary gland. The tumor was resected and the pathological diagnosis was phosphaturic mesenchymal tumor. A combination of systemic venous sampling and ⁶⁸Ga-DOTATOC PET/CT was useful in detection of a small FGF23-producing tumor. Precise tumor localization in such cases requires careful interpretation of scintigraphy.