Primary hyperparathyroidism (PHPT) in the dog is caused by excessive synthesis and secretion of parathyroid hormone (PTH) by abnormal chief cells of the parathyroid gland. This may be due to a parathyroid adenoma (85%), carcinoma (5.4%), or hyperplasia (12.4%). The excess secretion of PTH causes an increase in serum calcium due to mobilization from bone and resorption from the kidneys. Dogs with hypercalcemia usually present with PU/PD, lethargy, gastrointestinal signs, and changes in appetite; some have urolithiasis. Diagnosis of PHPT is made based on a persistently high ionized calcium and a normal or high PTH concentration, a serum PTHrP concentration of 0 pmol/L, serum phosphorus concentration within or less than the reference interval, ultrasonographic identification of a nodule on a parathyroid or thyroid gland, and exclusion of other causes of hypercalcemia, with no evidence of renal disease.

Ultrasound is typically used as a screening tool to identify abnormal parathyroid glands. Ultrasound accuracy can be limited by factors such as minimal gland enlargement, poor delineation of the gland’s borders, and the skill of the ultrasonographer. CT scan has superior tissue resolution, but the parathyroid glands are still hard to visualize due to size. CT with contrast enhancement was a useful tool in diagnosing parathyroid disease. Although CT scan was more accurate in identifying diseased parathyroid tissue, surgical exploration was able to identify additional nodules that the CT scan did not identify. 
Parathyroidectomy is the current treatment of choice for PHPT and has an overall cure rate of approximately 95%. Minimally invasive techniques such as ultrasound-guided ethanol ablation or heat ablation have been described but have a lower success rate of 70%–90%.^{1 2 3 4}