Parathyroid carcinoma presenting as severe hypercalcaemia responding to steroids

A man in his 50s was referred with profound, symptomatic hypercalcaemia. He was diagnosed with primary hyperparathyroidism, confirmed on (99m)Tc-sestamibi scan. He was treated for the hypercalcaemia and referred to ear, nose and throat (ENT) surgeons for parathyroidectomy, which was delayed due to the COVID-19 pandemic. In the ensuing 18 months, he had five hospital admissions with severe hypercalcaemia requiring intravenous fluids and bisphosphonate infusions. During the last admission, hypercalcaemia was resistant to maximal medical management. Emergency parathyroidectomy was planned, but delayed due to intervening COVID-19 infection. Due to persistent severe hypercalcaemia (serum calcium: 4.23 mmol/L), he was commenced on intravenous steroids, following which serum calcium normalised. Subsequently, he underwent emergency parathyroidectomy, which normalised his serum parathyroid and calcium levels. On histopathological examination, a diagnosis of parathyroid carcinoma was made. On follow-up, patient remained well and normocalcaemic. In patients with primary hyperparathyroidism unresponsive to standard therapy, but responsive to steroids, underlying parathyroid malignancy should be considered.