Phosphaturic Mesenchymal Tumor in the Proximal Femur Presenting as Tumor-induced Osteomalacia: A Case Report and Literature Review.

INTRODUCTION: An uncommon medical disorder known as tumor-induced osteomalacia (TIO) is characterized by severe hypophosphatemia, renal phosphate wasting, and osteomalacia due to a tumor. TIO has recently been linked to a particular kind of tumor known as phosphaturic mesenchymal tumor (PMT). PMTs release phosphatonins, such as fibroblast growth factor-23 (FGF23), which elevates serum levels of FGF23, leading to phosphate wasting and osteomalacia. However, due to their infrequent occurrence and vague symptoms, such as bone pain, myopathies, arthralgias, fractures, and weakness, the diagnosis of PMTs is often delayed or misdiagnosed. In this case report, a rare case of PMT in the proximal femur resulted in TIO, and it highlights the long and difficult journey from symptom onset to correct diagnosis and successful surgical management.

CASE REPORT: A 51-year-old woman endured persistent joint pain, muscle weakness, and fatigue for 2 years. Despite having no known health issues, she suffered from hip pain that spreads to her knees and ankles, and tingling and paresthesia in her legs, making it difficult to bear weight. She underwent surgery to remove a parathyroid adenoma, but unfortunately, her symptoms returned. Her magnetic resonance imaging revealed a lesion in her proximal femur, which was promptly removed. The tissue examination results verified the identity of the tumor as a PMT. The patient's phosphorus levels returned to normal and after a year of follow-up, she was able to resume normal daily activities, bear weight on the affected limb and showed no signs of the tumor recurrence.

CONCLUSION: Adult patients experiencing bone pain, progressive weakness, and multiple fractures with no family history of similar conditions should consider TIO as a potential cause. It is rare and often misdiagnosed and complete surgical removal of the tumor is the optimal treatment for TIO, resulting in the resolution of long-standing symptoms and biochemical abnormalities. Timely recognition, localization, and surgical removal of the tumor are crucial for symptom resolution and the restoration of normal bone mineralization.