MON-353 Tumor-Induced Osteomalacia from a Hypervascular Thoracic Paraspinal Mass: Challenges in Diagnosis and Management

• Published in: Journal of the Endocrine Society 2020-05, Vol.4 (Supplement_1)
• Main Authors: Perez, Paola M, Fu, Polly, Folick, Andrew, Ku, Gregory Michael, Shoback, Dolores M, Lee, Janet Yi Man
• Format: Article
• Language: English
• Subjects: Bone and Mineral Metabolism
• ISSN: 2472-1972; 2472-1972
• DOI: 10.1210/jendso/bvaa046.977

Background: Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome driven by ectopic production of fibroblast growth factor 23 (FGF23), resulting in renal phosphate wasting, hypophosphatemia, and bone demineralization. Successful therapy requires complete resection of the tumor, which is often challenging to localize. Clinical Case: A bedridden 37-year-old woman presented to Endocrine Clinic after 9 years of progressive pain and weakness in her back, hips, and extremities. She had previously been diagnosed with a neurodegenerative disease, though an MRI from 5 years ago showed bilateral subacute sacral ala fractures. CT scan on presentation showed generalized osteopenia and numerous subacute to chronic atraumatic fractures (involving ribs, scapula, pubic rami, and right femoral shaft) concerning for osteomalacia. On exam, she had profound lower extremity weakness. Laboratory testing was notable for serum phosphorus 0.6 mg/dL (normal (nl) 2.5-4.9), calcium 8.4 mg/dL (nl 8.5-10.5), PTH 216 pg/mL (nl 13-85), 25-OH vitamin D 26 ng/mL (nl 30-100), alkaline phosphatase 345 U/L (nl 45-130), 1,25-(OH)2 vitamin D 28 pg/mL (nl 18-72), renal tubular phosphorus reabsorption TmP/GFR 0.53 mg/dL (nl 2.97-4.45), and inappropriately normal FGF23 level 170 RU/mL (nl