ABSTRACT
Parathyromatosis is a rare cause of persistent or recurrent primary hyperparathyroidism and hypercalcemia due to the presence of hyperfunctioning foci of parathyroid tissue in the neck and/or mediastinum. We describe the case of a male patient who presented with severe hypercalcemia and a left-sided palpable parathyroid mass. Over the course of the next 18 years, the patient underwent neck exploration surgery on multiple occasions due to recurrent primary hyperparathyroidism and refractory hypercalcemia, complicated by nephrolithiasis and impairment of renal function, while bone mineral density was preserved. Histological findings and the natural course of the disease were consistent with parathyromatosis. Medical interventions with oral bisphosphonates or high-dose cinacalcet failed to control the patient's hypercalcemia. The combination of monthly denosumab and cinacalcet was, however, successful in maintaining the patient's serum calcium in the normal/upper-normal range over a 36-month period with no significant side effects. This is the first report of off-label denosumab use in combination with cinacalcet in the long-term management of parathyromatosis-related refractory hypercalcemia.