Delayed Hypocalcemia Post-Parathyroidectomy in a Dog with Parathyroid Carcinoma

Abstract

Hypocalcemia is considered a common electrolyte abnormality in dogs after parathyroidectomy and usually occurs within the first 2–4 days postoperatively. The authors describe a case involving an 11-year-old spayed female Chow Chow dog that presented with decreased appetite and ongoing hypercalcaemia, with an ionized calcium (iCa) level of 2.08 mmol/L. Computed tomography (CT) revealed enlargement of the left external cranial pole and right internal caudal pole of the parathyroid glands. Abdominal ultrasound identified multiple small hyperechoic mineralizations in both renal diverticula. These findings were consistent with primary hyperparathyroidism. Left cranial and right caudal parathyroidectomies were performed. Histopathological examination revealed proliferation of neoplastic neuroendocrine cells, highly suggestive of parathyroid carcinoma. ICa levels were monitored daily for 5 days, and no hypocalcemia was detected. However, on the 12^th postoperative day, the dog developed signs of hypocalcemia, including muscle twitching and tetany, and the iCa concentration dropped from 2.08 mmol/L to 0.6 mmol/L. The patient was treated with 10% calcium gluconate intravenously (1 ml/kg) for 3 consecutive days, followed by oral calcitriol (0.01 µg/kg twice daily) for 7 days. Clinical signs resolved, and ionized calcium levels increased to the normal range (1.45 mmol/L) within 4 days after initial oral calcitriol treatment. Subsequently, the calcitriol dose was tapered to once daily for 7 days, then every other day for the next 14 days, and ultimately discontinued after a total treatment duration of 4 weeks. Two weeks after discontinuation of calcitriol, the ionized calcium level remained within normal limits (1.26 mmol/L), and no signs of hypocalcemia were observed.