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

Surgical treatment for canine primary hyperparathyroidism is highly effective, with persistent hypercalcemia occurring in only 12.4% of cases.

This retrospective multicenter study evaluated outcomes following surgical treatment of primary hyperparathyroidism (PHPT) in 202 dogs across three academic veterinary hospitals from 2012 to 2022. The study aimed to characterize the proportion, causes, and definitions of persistent and recurrent hypercalcemia post-parathyroidectomy. The cohort had a mean age of 10.7 years with no sex predilection. Clinical signs attributable to hypercalcemia were present in 68% of cases. Histopathological diagnoses included parathyroid adenoma (58%), hyperplasia (24%), and carcinoma (7%). Dogs were stratified by follow-up duration: ≤6 months (Group 1, n=123) and >6 months (Group 2, n=79). Persistent hypercalcemia was identified in 12.4% (25/202) of dogs, with incorrect surgical excision and multiglandular disease as the primary contributing factors. Notably, preoperative ionized calcium and parathyroid hormone concentrations did not significantly differ between dogs with persistent versus resolved hypercalcemia, limiting their predictive utility. Recurrent hypercalcemia was rare, occurring in only 1.3% (1/79) of long-term follow-up dogs, associated with a new parathyroid mass. Fifteen dogs required a second surgical intervention and one required a third. These findings underscore that while surgical management of PHPT is generally effective, clinicians should maintain vigilance for multiglandular disease intraoperatively and ensure thorough parathyroid gland evaluation. Diligent perioperative planning, including careful surgical exploration and postoperative monitoring, is essential to minimize treatment failure.

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