Juvenile Hyperparathyroidism

By Tammy Hunter, DVM; Catherine Barnette, DVM.

What is juvenile hyperparathyroidism?

Juvenile hyperparathyroidism is a rare, inherited condition of German Shepherds. This condition causes the parathyroid glands, four small glands that are located in the neck near the thyroid gland, to produce abnormally large amounts of parathyroid hormone.

What is parathyroid hormone?

Parathyroid hormone, or parathormone (as it is sometimes called) is a hormone that regulates calcium levels in the blood.

When blood calcium levels are too low, parathyroid hormone is released from the parathyroid glands. Parathyroid hormone signals the bones to release calcium into the blood, and signals the kidneys to decrease the amount of calcium released in the urine. Parathyroid hormone also signals the gastrointestinal tract to absorb more calcium.

When blood calcium levels are high, the parathyroid glands slow their release of parathyroid hormone. Decreased levels of parathyroid hormone allow calcium to move back into the bones, allow more calcium to be excreted in the urine, and slow gastrointestinal absorption of calcium.

In a healthy animal, circulating levels of parathyroid hormone are constantly changing to accommodate calcium intake through food, calcium usage within the body, and other ongoing changes. The parathyroid glands are responsible for maintaining this delicate balance and keeping the blood calcium concentration within an optimal range.

What are the effects of juvenile hyperparathyroidism?

Juvenile hyperparathyroidism causes a constant state of elevated parathyroid hormone, affecting calcium and phosphorus balance within the body. Elevated circulating parathyroid hormone leads to constant release of calcium from the bones, resulting in abnormal bone development and stunted growth. Because of the effects of parathyroid hormone on the kidneys, dogs with juvenile hyperparathyroidism often have increased thirst and urination.

What causes juvenile hyperparathyroidism?

Juvenile hyperparathyroidism is an inherited, autosomal recessive trait. This means that affected dogs must carry two defective copies of the gene, one inherited from each parent.

It is uncommon for dogs with juvenile hyperparathyroidism to have parents who are clinically affected by the disease; once a dog is diagnosed with the condition, they typically are not bred. More often, both parents of a dog with juvenile hyperparathyroidism are carriers of the disease. These carrier dogs should not be bred again in the future. Additionally, siblings of an affected dog should not be bred; each sibling of an affected dog has a 50% chance of being a carrier of juvenile hyperparathyroidism.

The first documented cases of juvenile hyperparathyroidism were diagnosed in German Shepherds and they continue to be the breed most commonly diagnosed with this condition.

How is juvenile hyperparathyroidism diagnosed?

The first sign of juvenile hyperparathyroidism is usually stunted growth. While evaluating your puppy to determine the cause of this problem, your veterinarian may perform a number of tests.

Radiology: X-rays of dogs with juvenile hyperparathyroidism show changes in the appearance of the bones, due to a decrease in bone density.

Bloodwork: Bloodwork of a dog with juvenile hyperparathyroidism will show calcium levels that are significantly above normal. These dogs may also have abnormally low phosphorus levels, though this is not always the case.

Confirmatory testing: If your veterinarian suspects juvenile hyperthyroidism based on x-rays and bloodwork, he will confirm the diagnosis by measuring the level of parathyroid hormone in your dog’s blood. This is a special test that will be sent to an outside laboratory. It may take several days to receive results from this test. If your dog has an abnormally high level of parathyroid hormone in the blood, this will confirm the diagnosis of juvenile hyperparathyroidism.

How is juvenile hyperparathyroidism treated?

Juvenile hyperparathyroidism is typically treated with surgery. Each dog is born with four parathyroid glands; removal of anywhere from one to three of the parathyroid glands is performed to bring the calcium levels into a more normal range. This may require multiple surgeries, in order to achieve the correct calcium balance. With surgery, the prognosis for this condition is typically good.

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