7999 Tumor Induced Osteomalacia Caused By Glomangiopericytoma

Abstract Disclosure: N. Kabir: None. E. Campbell: None. S. Singh: None. Introduction: Tumor induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused primarily by FGF-23 secreting tumors. Excessive production of FGF23 causes hypophosphatemia, decreased phosphate resorption in the gut, increased renal phosphate wasting, and decreased activation of Vitamin D. This leads to decreased bone density, bone pain, proximal muscle weakness, impaired gait, and recurrent fractures. Case Presentation: 44 year old male with a history of recurrent insufficiency fractures and weakness. At the time of evaluation, he reported fracture of tibial growth plate, sacral fracture, and metatarsal stress fracture. Other symptoms included bone pain, fatigue, muscle weakness, and intercostal muscle spasms with exertion. His pain was debilitating, requiring crutches to ambulate. Available labs at that time were significant for hypophosphatemia (1.3 mg/dL), elevated ALP (160 U/L), low 25OH-vitamin D (26 ng/mL), and normal calcium (8.7 mg/dL). Urine studies demonstrated phosphaturia (fractional excretion of phosphate, 62.4%). FGF23 level resulted at the upper limit of normal (210 RU/mL). Pending further evaluation, burosumab was started. Further work up included a 68Ga-PET-DOTATATE scan revealing a somatostatin receptor expressing soft tissue mass in the left sphenoid sinus and posterior left ethmoid sinus. The scan also demonstrated impending bilateral femur fractures, prior rib fractures, and sacral insufficiency fractures. Based on these findings, he was admitted to the hospital and underwent prophylactic, intramedullary nail fixation of his bilateral femur fractures. He underwent resection of skull base tumor with the final pathology revealing a sinonasal glomangiopericytoma. Immunohistochemical stain was positive for CD99 and cyclin D1, and focally positive for SMA, consistent with histopathologic diagnosis. Patient required prolonged inpatient rehabilitation to recover independent ambulation. Discussion: Sinonasal glomangiopericytoma (SNGP) is a mesenchymal tumor that accounts for <0.5% of all nasal and sinus tumors. TIO due to SNGP is extremely rare, with only a few cases reported since the 1990s. As seen with our patient, TIO from SNGP rarely presents with sinonasal symptoms, and can often be overlooked. Our patient hadb significant progression of disease and disability due to numerous delays in diagnosis and management. Definitive cure for TIO can be achieved with complete surgical resection of the tumor, but failure to diagnose in a timely manner can result in decline in quality of life. Our takeaway from this case is that providers should obtain FGF23 levels, especially in the setting of hypophosphatemia and phosphaturia, to complete the work up for osteomalacia. Presentation: 6/1/2024