Rebound Hypercalcemia After Denosumab Cessation in Adult Fibrous Dysplasia: A Case Report and Clinical Alert.

Background: Fibrous dysplasia (FD) is a rare congenital bone disease. Denosumab, a monoclonal antibody targeting nuclear factor kappa-B ligand (RANKL), suppresses osteoclast activity and exhibits therapeutic potential for FD. Case Presentation: We present the case of an adult female patient diagnosed with FD who had undergone 7 treatment cycles of denosumab (120 mg/dose, sc.) with a cumulative dose of 840 mg. After discontinuing denosumab for 7 months, the patient experienced a crisis of rebound hypercalcemia. Conclusion: Although, rare reports of hypercalcemia induced by discontinuation of denosumab are primarily seen in adolescents. By reporting this case, we aim to alert clinicians to the risk of rebound hypercalcemia in adult patients with FD undergoing denosumab treatment.