Hyperparathyroidism in Dogs and Cats
Hyperparathyroidism is a disease of the parathyroid glands that results in overproduction of parathyroid hormone. Because this hormone controls calcium and phosphorous levels, an excess of it can result in elevated blood calcium levels, causing increased thirst and urination, weakness, nausea, vomiting, and more. Surgery is the only way to treat the disease and involves the removal of at least one parathyroid gland. The Keeshond is the most commonly affected breed.
OverviewHyperparathyroidism is an uncommon disease that affects calcium and phosphorus regulation in dogs, and less commonly, in cats. It occurs when some or all of the body’s four parathyroid glands excessively produce parathyroid hormone, ultimately leading to extremely high blood calcium levels.
The condition can either be primary or secondary, though only the primary form will be discussed here. Primary hyperparathyroidism may be caused by a benign, parathyroid hormone-secreting tumor, called an adenoma, on one or more of the parathyroid glands, or less commonly, by a cancerous tumor. Parathyroid hyperplasia, a condition where several parathyroid glands become enlarged, can also cause hyperparathyroidism. In rare cases, a hereditary neonatal form hyperparathyroidism can occur in German Shepherds.
Symptoms and IdentificationMany pets with hyperthyroidism may not show signs until the blood calcium levels become extremely high.
Signs primarily affect the gastrointestinal, urinary, and neuromuscular systems. Bones may also come under attack, as their calcium reserves are depleted in order to increase calcium levels in the blood.
Dogs with hyperparathyroidism will usually exhibit a gradual onset of symptoms, including:
- Increased thirst, increased urination, and/or urinary incontinence
- Weakness, stiffness, decreased muscle mass, and/or lethargy
- Inappetence, nausea, vomiting, and/or constipation
Affected BreedsPrimary hyperparathyroidism usually occurs in older dogs. Keeshonds are most likely to be affected, and Siamese cats may be predisposed to the condition. In rare cases, German Shepherds may experience the neonatal version of primary hyperparathyroidism.
TreatmentTreatment is usually accomplished surgically. If a parathyroid tumor is present, the affected gland is removed and biopsied. If parathyroid hyperplasia is diagnosed, one to three of the glands can be removed to achieve normal calcium levels. More than one surgery may be necessary to get to the right calcium balance, though one parathyroid gland is always left behind to carry out normal functions.
Dogs that have extremely high calcium levels may require hospitalization with fluid therapy and close electrolyte management before and after surgery.
As an alternative to surgery, there are less invasive ultrasound-guided procedures that use ethanol or heat to destroy the cells that are overproducing parathyroid hormone. However, these procedures require specialized skills and may not be offered at most veterinary clinics.
PreventionThere is no known means of prevention, save genetic counseling to encourage the removal of affected dogs from the breeding pool. For Keeshonds, genetic testing at Cornell University’s School of Veterinary Medicine can determine carrier status in order to remove affected animals from breeding programs.
This article has been reviewed by a Veterinarian.