ODP083 Burosumab Treatment for Fibrous dysplasia/McCune-Albright Syndrome with Severe Spine Deformity

INTRODUCTION: Fibrous dysplasia/McCune-Albright Syndrome (FD/MAS) is a rare multi-endocrine disorder with bone abnormalities called polyostonic fibrous dysplasia, presumably related to fibrous growth factor 23 (FGF23). We present a case of a patient with FD/MAS who successfully underwent spinal fusion surgery after efficacious anti-FGF23 treatment using its monoclonal antibody (burosumab). CLINICAL CASE: A late teenage boy, clinically diagnosed with FD/MAS, was referred to our hospital for possible treatment of burosumab, because he desperately needed promising medical intervention for bisphosphonate-resistant severe polyostonic fibrous dysplasia with enormously high turnover bone disease. On presentation, he had severe scoliosis (>80 degree-thoracic spine curve) with mild hypophosphatemia (2.5 mg/dL), low 25-hydroxyvitamin D (7.3 ng/mL), normal corrected calcium (9.6mg/dL) and high intact PTH (95.7 pg/mL). His FGF23 level was 90.4pg/mL, which was inappropriately high. He had a history of previous bilateral hip fractures with partially removed Café au macules on the back. Baseline laboratory findings revealed no remarkable signs of endocrinopathies, whereas serum bone markers were remarkably high (tartrate-resistant acid phosphatase 5b, >1500 mU/dL; procollagen type 1 N-propeptide, >1200 ng/mL, alkaline phosphatase, 2638 U/L). He was started on monthly 50mg of burosumab therapy subcutaneously. Interestingly enough, his alkaline phosphatase levels gradually decreased down to 1619 U/L at month 6 post-anti-FGF23 treatment. Subsequent spine fusion surgery was successfully underwent with his thoracic curve corrected by instrumentation. DISCUSSION: This is, to our knowledge, the first case with FD/MAS, who was given monthly burosumab, followed by orthopedic spinal instrumentation to straighten the spine curve. Burosumab treatment for FD/MAS may enhance bone flexibility by blocking abnormal FGF23-related signaling, enabling safer approach to promising orthopedic surgeries. Presentation: No date and time listed