Hyperparathyroidism

Summary

Hyperparathyroidism is an uncommon disease of abnormal calcium and phosphorus regulation in dogs. It occurs when one or all of the body's four parathyroid glands produce too much parathyroid hormone. Ultimately, this leads to very high blood calcium levels.

Hyperparathyroidism can be termed primary or secondary. For the purposes of this genetic disease discussion, only the primary (hereditary) forms will be discussed.

Primary hyperparathyroidism occurs 1) as a result of either a benign, parathyroid hormone-secreting tumor (adenoma) on one of the four, thyroid gland-associated parathyroids or 2) due to a congenital disease of the parathyroid glands that allows for excessive production of parathyroid hormone.

Juvenile hyperparathyroidism is inherited as an autosomal recessive trait.

Symptoms and Identification

Symptoms will primarily affect the gastrointestinal, urinary, and neurologic systems--as well as the calcium-rich bones--as the body's calcium reserves are tapped to increase blood levels of this mineral.

Dogs with hyperparathyroidism will usually exhibit a gradual onset of a variety of symptoms associated with excessive levels of calcium in the bloodstream:

• Increased thirst and urination and/or abnormal urination

• Weakness, stiffness, decreased muscle mass and/or lethargy

• Inappetance, nausea, vomiting and/or constipation

With the juvenile form of the disease dogs are identified once abnormal (stunted) growth is noted. The above signs associated with the adenoma form may be present as well.

Diagnosis is usually achieved by finding high calcium levels in the blood and correlating this finding with the medical history, other blood tests, X-rays, urinalysis, EKG and an ultrasound of the neck to check for a mass on one of the four parathyroid glands.

Affected Breeds

Keeshonds are the principal breed predisposed to primary hyperparathyroidism as a result of benign parathyroid gland tumors. German Shepherds, however, are most likely to suffer the rarer, juvenile version of primary hyperparathyroidism.

Treatment

Treatment for hyperparathyroidism is usually accomplished surgically. If a parathyroid adenoma is present, the affected parathyroid gland is removed and biopsied. If juvenile parathyroidism 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 in these cases. One parathyroid gland is always left behind to carry out normal functions. management.

Dogs who present with extremely high calcium levels may require hospitalization with fluid therapy and close electrolyte management.

Veterinary Cost

The cost of diagnosis typically ranges between $200 and $1,000, depending on whether an ultrasound is performed. A requirement for intensive care upon presentation will inevitably increase the cost of diagnosis significantly. Similarly, surgical intervention is an expensive affair given that board-certified surgeons are often employed to handle this delicate surgery. $1,500 to $3,000 is the typical outlay for this procedure.

Prevention

There is no known means of prevention save genetic counseling which would serve to eliminate affected dogs from the breeding pool. For keeshonds, genetic testing is available via Cornell University's School of Veterinary Medicine to determine carrier status so as to appropriately remove these animals from breeding programs.

Juvenile hyperparathyroidism is prevented by preventing affected dogs and their first degree relatives from breeding.

References

Greco, D.S. 1995. Pediatric Endocrinology. In J.D. Bonaguara and R.W. Kirk (eds.) Kirk's Current Veterinary Therapy XII Small Animal Practice. p 346-351. W.B. Saunders Co., Toronto.