A 65-year-old male with phosphaturic mesenchymal tumor presenting as tumor-induced osteomalacia: a case report

Introduction and importance: Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disorder caused by phosphaturic mesenchymal tumors (PMTs), characterized by chronic hypophosphatemia and impaired bone mineralization. Case presentation: A 65-year-old man presented with progressive bone pain lasting 3 years. Laboratory results showed persistent hypophosphatemia and elevated fibroblast growth factor 23. Imaging revealed a hypermetabolic lesion in the left acetabulum. The tumor was surgically resected, and histology confirmed a spindle cell neoplasm without vascular invasion. Serum phosphorus normalized postoperatively, and the patient showed sustained clinical improvement over 1 year. Clinical discussion: This case underscores the diagnostic challenges of TIO, often mimicking other metabolic bone diseases and leading to significant delays. Compared with similar reports, our case highlights the utility of combined positron emission tomography and magnetic resonance imaging in localizing PMTs and the dramatic clinical improvement following resection. Conclusion: This case underscores the importance of recognizing TIO early to enable effective treatment and avoid prolonged morbidity.