Endocrine Abstracts

Case 1: A 65-year-old man was admitted with symptomatic hypocalcaemia (corrected calcium of 1.65 mmol/l, PTH 46.6 (1.6–6.8) pmol/l, and vitamin D 51.4 (50–150) nmol/l)) 5 days following denosumab initiation. He had a diagnosis of probable urothelial carcinoma with associated osteoblastic metastases, and 10 days prior to this admission had been treated for hypercalcaemia (corrected calcium of 3.04 (2.20–2.60) mmol/l) with i.v. fluids following which denosumab was initiated. His hypocalcaemia improved with i.v. calcium infusions, but he became significantly hypocalcaemic whenever i.v. calcium was stopped. He required a total of 550 ml of 10% calcium gluconate intravenously with concomitant oral calcium supplementation to improve his hypocalcaemia. After discharge he was maintained on 2.7 g of oral calcium for 2 months following which it was possible to wean off treatment.

Case 2: A 73-year-old woman presented with paraesthesia and severe hypocalcaemia (corrected calcium 1.46 mmol/l), which was associated with an elevated PTH (54.8 pmol/l), and vitamin D deficiency (17.6 nmol/l). She had a history of breast cancer with skeletal metastases, which was treated with denosumab for 4 months up until admission. She required a total of 800 ml of 10% calcium gluconate infusions and oral calcium supplementation during a prolonged 27-day admission due to rapid recurrence of hypocalcaemia on cessation of i.v. calcium infusions. She remained eucalcaemic on 2 g of oral calcium daily and 40 000 units of colecalciferol monthly following discharge.

Discussion: Hypocalcaemia is a recognised complication of denosumab therapy, where fatal cases have been reported in the literature. The above cases highlight the need for close serum calcium monitoring to allow prompt correction of hypocalcaemia. Owing to its long half-life, presentation of hypocalcaemia following denosumab therapy can be prolonged, leading to protracted inpatient admissions requiring aggressive i.v. calcium replacement. It is also prudent to identify and correct potential risk factors such as vitamin D deficiency prior to initiation of denosumab.