Tumor-induced hypophosphatemic osteomalacia caused by a mesenchymal tumor of the mandible managed by a segmental mandibulectomy and microvascular reconstruction with a free fibula flap

Background: Tumor-induced osteomalacia is a rare paraneoplastic syndrome in which patients develop hypophosphatemia and osteomalacia. Methods and Results: Here, we report a unique case of a 42-year-old man who presented to our institution with a 1-year history of pain in his ribs, hips, lower back, and feet. Radiologic examination revealed a decrease in bone density and multiple insufficiency fractures. Laboratory evaluation revealed hypophosphatemia, low serum 1,25 dihydroxy vitamin D₃, and elevated fibroblast growth factor 23 (FGF23). A positron emission tomography/CT scan showed increased uptake in the right mandibular third molar region. Panoramic radiography and CT scanning showed a lytic expansile bone lesion. A mandibular bone biopsy revealed a mixed connective tissue tumor. A right segmental mandibulectomy was performed, followed by microvascular reconstruction. The resection was confirmed by normalization of serum phosphate and FGF23. Conclusion: Successful management of this condition was achieved, with complete surgical resection of the tumor and reconstructive surgery.