Osteomalacia tumoral como causa de fracturas espontáneas

Abstract

Tumor-induced osteomalacia is a rare paraneoplastic syndrome characterized by chronic hypophosphatemia secondary to renal phosphate wasting mediated by excess fibroblast growth factor 23 (FGF23). Diagnostic delay is common due to the nonspecific clinical presentation and the difficulty in localizing the causative lesion. Case report: A previously healthy 36-year-old man presented with progressive low back pain for more than 3 years and was admitted after right hip trauma. Laboratory evaluation showed serum phosphate 0,5 mg/dL, parathyroid hormone 269 pg/mL, bone-specific alkaline phosphatase 139 µg/L, and a tubular maximum for phosphate reabsorption per glomerular filtration rate of 1.24 mg/dL. Initial radiographic studies revealed Looser–Milkman pseudofractures in the left hip and a right intertrochanteric fracture. Given the suspicion of tumor-induced osteomalacia, FGF23 was measured and was 130.6 pg/mL Subsequently, PET/TC 68Ga-DOTATATE identified a femoral nodular lesion measuring 58,5×16 mm, with a maximum SUV of 27.9, which was confirmed by magnetic resonance imaging. Treatment with phosphate, calcitriol, and calcium was initiated, with partial response. Congenital hypophosphatemic rickets was excluded. Because of vascular invasion, resection was incomplete. Histopathology demonstrated a spindle-cell and epithelioid mesenchymal tumor with osteoclast-like giant cells, and FISH identified an FN1–FGFR1 fusion. Therapeutic alternatives are currently under evaluation. Conclusion: Tumor-induced osteomalacia should be suspected in patients with fragility fractures and persistent hypophosphatemia. Its diagnosis requires specialized biochemical testing and molecular imaging for tumor localization. This case highlights the importance of a timely biochemical and therapeutic approach.