Summary: Hypercalcemia due to parathyroid carcinoma (PC) is safely and quickly controlled with rapidly increasing evocalcet doses. Most parathyroid carcinomas are detected because of hypercalcemia due to primary hyperparathyroidism (PHPT). Hypercalcemia becomes more severe in patients with PC than those with parathyroid adenoma or hyperplasia. Hypercalcemia often causes renal dysfunction, gastrointestinal symptoms, and psychiatric symptoms. Consequently, the serum calcium level needs to be promptly corrected. Here, we report a case of PC with remarkably persistent hypercalcemia, which we safely and quickly controlled with rapidly increasing evocalcet doses. A 77-year-old female presented with renal dysfunction. Her serum calcium (Ca) and intact parathyroid hormone serum levels were 13.9 mg/dL and 1.074 pg/mL, respectively. Her renal function worsened because of hypercalcemia due to PHPT. Technetium-99 m methoxy-isobutyl-isonitrile parathyroid scintigraphic examination revealed an accumulation below the right thyroid lobe. CT examination showed a 35-mm mass. Hypercalcemia needed to be immediately corrected because of the patient's worsening renal function. Evocalcet treatment at a gradually increasing dose of up to 20 mg over 3 weeks allowed her serum Ca level to be maintained below 11 mg/dL. Only mild nausea was observed at the beginning of the treatment. The mass was suspected as PC because the hypercalcemia was refractory to high-dose evocalcet. The patient was treated with parathyroidectomy and ipsilateral thyroidectomy. PC was diagnosed based on the pathological findings of capsular and venous invasion. The patient's renal function improved and surgery could be safely performed by promptly correcting hypercalcemia.
Learning points: Hypercalcemia due to parathyroid carcinoma (PC) is often more severe than that caused by parathyroid adenoma or hyperplasia. PC is a rare disease, but it should be considered if the patient has intractable hypercalcemia due to primary hyperparathyroidism (PHPT). Evocalcet, which is used to treat hypercalcemia due to PHPT, does not interact with P450 (CYP) and causes few side effects. Complications, including renal dysfunction, were improved and the surgery could be safely performed by promptly correcting hypercalcemia. PC has a high recurrence rate. En-block excision is necessary when PC is suspected.