Persistent and recurrent hypercalcemia are uncommon in dogs undergoing surgical treatment for primary...

To report the proportion of cases, causes, and definitions of recurrent and persistent hypercalcemia in dogs following surgical removal of autonomously functioning parathyroid tissue.

Retrospective review of medical records from 3 academic veterinary hospitals (2012 to 2022) identified dogs with surgically treated primary hyperparathyroidism. Data included signalment, clinical signs, diagnostics, treatment, histopathology, and outcomes. Dogs were categorized by follow-up: ≤ 6 months (group 1) or > 6 months (group 2). Descriptive statistics were performed. The Mann-Whitney U test compared preoperative ionized calcium and parathyroid hormone between dogs with persistent versus resolved hypercalcemia.

202 dogs met the inclusion criteria. Group 1 included 123 dogs, and group 2 included 79 dogs. Mean age was 10.7 ± 2.23 years, with no sex predilection. Hypercalcemia-associated clinical signs occurred in 68% (138 of 202) of dogs. Histopathology revealed parathyroid adenoma (58% [135 of 233]), hyperplasia (24% [56 of 233]), and carcinoma (7% [10 of 233]) as most common. Persistent hypercalcemia occurred in 25 of 202 dogs (12.4%), primarily due to incorrect surgical removal or multiglandular disease. Preoperative ionized calcium and parathyroid hormone did not differ between persistent and resolved cases. Recurrent hypercalcemia occurred in 1 of 79 (1.3%) dogs in group 2, associated with a new mass. Fifteen dogs underwent a second surgery; 1 dog required a third surgery.

Persistent and recurrent hypercalcemia were uncommon (12.4% and 1.3%, respectively). Multiglandular disease and incorrect surgical excision were the leading causes of persistent hypercalcemia.

This study emphasizes that persistent and recurrent hypercalcemia are uncommon but require diligent perioperative planning and monitoring.