Symptomatic Rebound Hypercalcemia After Denosumab Discontinuation in a Pediatric Patient With Cherubism

Abstract

Background: Pediatric bone diseases due to osteoclast overactivity have limited therapeutic options. Denosumab, a human monoclonal antibody against RANK-ligand, has been used in the treatment of these conditions despite limited pediatric safety data. Rebound hypercalcemia after denosumab cessation is a rare and potentially serious complication in children with an unpredictable course (1). We present the first report of a child with cherubism who experienced acute symptomatic hypercalcemia five months after denosumab cessation. Clinical Case: An 11 year old male presented to our emergency department (ED) with 2 weeks of nausea, vomiting, abdominal pain, and bilateral leg pain. He was diagnosed with cherubism at age 3 years with progressive painless bilateral jaw swelling, teeth crowding, and proptosis. His bilateral maxilla and left mandible were debulked between ages 5-8 years due to tumors causing dyspnea. The resected tumors showed RANK-ligand expression. Thus, he started a 1-year course of denosumab 80 mg monthly subcutaneous injections for additional lesions not amenable to surgery with marked clinical and radiographic improvement. He had mild hypocalcemia during denosumab therapy, for which he received cholecalciferol 2000 IU and calcium citrate total 1500 mg per day. Calcium citrate was stopped with corrected serum calcium (Ca) 10.1 mg/dL (8.8-10.8 mg/dL) three months prior to ED visit. His presentation to ED five months after denosumab revealed marked hypercalcemia (corrected Ca 13.9 mg/dL), iPTH 5.4 pg/mL (7.5-53.5 pg/mL), 25-OH vitamin D 19 ng/mL (30-100 ng/mL), and hypercalciuria (urine Ca/creatinine ratio 0.58 mg/mg, normal <0.2 mg/mg) concerning for rebound hypercalcemia post-denosumab therapy. He received IV hyperhydration, furosemide, calcitonin, and IV pamidronate 0.5 mg/kg. At discharge, corrected Ca was 8.7 mg/dL. One week later he developed acute nausea and vomiting. Laboratory tests again showed hypercalcemia (Ca 13.3 mg/dL) and hypercalciuria. He received one dose of IV zoledronic acid at 0.025 mg/kg with resolution of hypercalcemia. He remains normocalcemic, normocalciuric, and asymptomatic two months after zoledronic acid treatment. Conclusion: This is the first case, to our knowledge, of a pediatric patient with cherubism with acute symptomatic hypercalcemia after denosumab treatment, reinforcing the need for frequent calcium monitoring months after cessation. Zoledronic acid is also shown to effectively treat rebound hypercalcemia after denosumab cessation. Larger studies are needed to further evaluate denosumab use and safety in pediatric bone diseases with osteoclast overactivity. Reference: (1)Upfill-Brown A, Bukata S, Bernthal NM, Felsenfeld AL, Nelson SD, Singh A, Wesseling-Perry K, Eilber FC, Federman NC. Use of Denosumab in Children With Osteoclast Bone Dysplasias: Report of Three Cases. JBMR Plus. 2019 Aug 22;3(10):e10210