Tumor induced osteomalacia: a rare case report

Abstract

Tumor-induced osteomalacia is a rare paraneoplastic syndrome caused by excessive fibroblast growth factor 23 (FGF23) secretion from phosphaturic mesenchymal tumors, leading to hypophosphatemia and osteomalacia. We present a 36-year-old female with progressive bilateral hip pain and pathological femoral neck fractures without trauma history. Despite being treated for hyperparathyroidism, she developed progressive mobility decline, becoming bedridden. Laboratory investigations revealed persistent hypophosphatemia (1.1-1.8 mg/dl) and elevated FGF23 levels (131.50; normal: 23.20-95.40). Parathyroid scanning was negative, but Ga-68 DOTA scan identified a somatostatin receptor-expressing lesion in the left superior gingivobuccal sulcus. Following complete surgical excision and endocrine treatment, serum phosphorus normalized (3.8 mg/dl), fractures healed progressively, and the patient regained independent mobility within seven months. This case emphasizes the importance of considering tumor-induced osteomalacia in adults with unexplained bone pain, pathological fractures, and hypophosphatemia, highlighting the diagnostic value of FGF23 measurement and functional imaging for successful management.