Tumor induced-osteomalacia caused by a phosphaturic mesenchymal tumor in the sartorius muscle: a case report

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome resulting from excessive secretion of fibroblast growth factor-23 (FGF23) by phosphaturic mesenchymal tumors (PMTs). We report the case of a 35-year-old man with a three-year history of progressive musculoskeletal symptoms and severe mobility impairment, who had not received a correct diagnosis during this period. Laboratory evaluation revealed severe hypophosphatemia and elevated FGF23 levels. Magnetic resonance imaging (MRI) and 68 Ga-DOTA-TATE PET/CT identified a metabolically active lesion in the sartorius muscle. Surgical resection of the tumor resulted in complete resolution of symptoms, restoration of mobility and normalization of phosphate metabolism. This case emphasizes the importance of considering TIO in patients with unexplained osteomalacia and highlights the diagnostic value of functional imaging.