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Abstract Disclosure: M.M. Eid: None. S. Reutrakul: None. Introduction: Denosumab is a fully human monoclonal antibody that binds to the receptor activator of nuclear factor kappa Β ligand, blocks osteoclast function and reduces bone resorption. Case: A 91 year old male with history of osteoporosis, type 2 diabetes, chronic kidney disease (CKD) and prostate cancer. Presented with fatigue and cold intolerance. Denied confusion, muscle cramp, perioral numbness/tingling, bowel habit change. Medications included empagliflozin 12.5 mg/day, leuprorelin 45 mg every 6 months since 2021 and cholecalciferol 1000IU/day. On examination, he was alert and oriented x 3 with stable vital signs. No thyromegaly. Chvostek's sign was negative. Labs: serum calcium (Ca) 6.5 mg/dl, corrected Ca (Co Ca) 6.7mg/dl(N 8.7-10.4), ionized Ca 0.7mMol/l (N 1.13-1.32), TSH 131uIU/ml (N 0.55-4.78), free T4 0.72ng/dl (N 0.89-1.76), creatinine 1.55mg/dl, GFR 42ml/min/1.73m2, HbA1C 6.1%. EKG with corrected QT interval of 499 msec. Hypocalcemia work up : parathyroid hormone (PTH) 762 pg/ml (N 18.4-80.1), 25 OH vitamin D (Vit D) 37ng/ml (N 30-100), 1,25 OH Vit D 77pg/ml (N 18-72), phosphorus (Phos) 1mg/dl (N 2.4-5.1), magnesium (Mag) 1.7mg/dl (N 1.6-2.6),ALP 59U/L(N 45-117). Clinical impressions were a new diagnosis of primary hypothyroidism and non PTH mediated hypocalcemia with secondary hyperparathyroidism. A thorough review of medication revealed that he received the first dose of denosumab 60 mg 4 months prior to this presentation. Baseline labs 1 month prior to denosumab: Ca/Co Ca 9.1/9.2mg/dl, Phos 4.5mg/dl, PTH 199.6pg/ml, Mag 2.1mg/dl,TSH 2.72 uIU/ml. 2 months after denosumab administration, serum Ca/Co Ca 8.8/8.6mg/dl. He was admitted and received Ca gluconate 2gm IV pushes, calcitriol 0.5 mcg/day and levothyroxine 50 mcg/day and kept on cardiac monitoring. He remained asymptomatic. On the 5th day, serum Ca/Co Ca 8.4/8.6mg/dl, Phos 3mg/dl, Mag 2mg/dl. He was discharged on oral Ca Carbonate, calcitriol and levothyroxine. The second denosumab dose was cancelled. Conclusion: Denosumab is an effective anti-osteoporotic medication but can cause hypocalcemia. The risks for denosumab induced hypocalcemia include renal impairment, Vit D deficiency and lack of Ca/Vit D supplementation. Hypocalcemia usually occurs 1 - 2 weeks after denosumab, corresponding to its peak of action. Checking serum Ca and Vit D with correction of deficiencies before starting denosumab is recommended. In high risk patients with CKD, daily Ca and Vit D supplements are recommended (1). Our case has CKD and developed severe hypocalcemia and hypophosphatemia 4 months after receiving denosumab without other apparent causes for hypocalcemia. Hypothyroidism is likely an incidental diagnosis and not contributing to hypocalcemia in the absence of rhabdomyolysis. Reference: 1.Jalleh R, Basu G, Leu RL, Jesudason S: Denosumab induced severe hypocalcemia in chronic kidney disease. Case Rep Nephrol.2018 Presentation: 6/2/2024
Eid et al. (Tue,) studied this question.