Parathyroid Carcinoma Complicated by Parathyromatosis and Refractory Hypercalcemia.

Parathyroid carcinoma (PC) is a rare malignancy. In January 2022, a 41-year-old woman presented with weight loss, proximal muscle weakness, and bone pain. She was diagnosed with severe hypercalcemia with serum calcium of 15.5 mg/dL (8.8-10.6 mg/dL). A biopsy of cervical lymphadenopathy revealed non-caseating granulomatous lymphadenitis. Primary hyperparathyroidism was subsequently confirmed with parathormone (PTH) exceeding 2,500 pg/mL (12-88 pg/mL), leading to left-superior parathyroidectomy and hemithyroidectomy. Histopathology suggested PC versus adenoma, with oxyphilic cells. Postoperatively, she manifested severe hypocalcemia and vitamin D deficiency alongside elevated PTH levels. In January 2023, she experienced a hypercalcemic crisis and developed a new right-sided neck mass. Wide excision revealed PC with parathyromatosis. By September 2023, another hypercalcemic crisis and new left cervical nodules necessitated further surgery, confirming PC deposits in the neck, though without lymph node metastases. Despite treatment with cinacalcet and zoledronic acid, her hypercalcemia persisted until denosumab produced a dramatic response (serum calcium dropping from 16.7 to 7.9 mg/dL; PTH 1,168 pg/mL). However, she remains at risk for progressive local disease and potential distant metastases.