Primary hyperparathyroidism is uncommon in large animals. The objective of this study was to describe the diagnostic findings and efficacy of treatment in equids with primary hyperparathyroidism.
Cases were recruited by retrospective review of records at Cornell University and via an ACVIM listserv query. Inclusion criteria were an equid with hypercalcemia and one or more of the following: 1) high parathyroid hormone (PTH); 2) normal PTH with high calcium and negative PTH-related protein; or 3) histopathologic identification of a parathyroid adenoma.
Sixteen horses and one mule fulfilled the inclusion criteria. The most common presenting complaints included weight loss (12), hypercalcemia (10), anorexia (6), and colic (2). The median ionized calcium at presentation was 2.66 mmol/L (range, 2.14 – 4.95 mmol/L; reference range 1.58 – 1.9 mmol/L), and the median PTH concentration was 23.7 pmol/L (range: 3.8 – 128.63 pmol/L; reference range 0.6 – 11 pmol/L). Suspected abnormal parathyroid tissue was localized in 12/17 equids by ultrasonography (7/13) and/or technetium 99m sestamibi scintigraphy (10/11). Five out of five successfully excised tumors were located at the thoracic inlet, and surgery resulted in complete cure. One peri-thyroid tumor was excised; however, the horse remained hypercalcemic following surgery. Four additional cases treated surgically, five treated medically, and two not treated also remained hypercalcemic.
Parathyroid adenomas in equids can be successfully localized with ultrasonography and/or scintigraphy. Surgical excision appears more likely to be successful if a single abnormal gland is identified at the thoracic inlet.
Large Animal Internal Medicine Resident
Cornell University School of Veterinary Medicine
Thursday, June 14
1:30 PM – 1:45 PM
Friday, June 15
2:15 PM – 2:30 PM
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