What is juvenile hyperparathyroidism?
Juvenile hyperparathyroidism is a rare, inherited condition of German shepherds. This condition causes the parathyroid glands to produce abnormally large amounts of parathyroid hormone. These four small glands are in the neck, near the thyroid gland.
What is parathyroid hormone?
Parathyroid hormone, sometimes called parathormone, is a hormone that primarily regulates calcium levels in the blood, but also affects phosphorus levels.
When blood calcium levels are too low, the parathyroid glands release parathyroid hormone. This hormone signals the bones to release calcium into the blood. It signals the kidneys to decrease the calcium released in the urine while inhibiting the reabsorption of phosphorus. Parathyroid hormone also signals the gastrointestinal tract to absorb more calcium as a result of vitamin D creation from the kidneys.
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 and phosphorus concentrations 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, leading to an abnormal gait. Dogs with juvenile hyperparathyroidism often have increased thirst and urination due to the effects of parathyroid hormone on the kidneys. Other clinical signs can include urinary incontinence, listlessness or weakness, and loss of appetite.
What causes juvenile hyperparathyroidism?
Juvenile hyperparathyroidism is an inherited, autosomal recessive trait. 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. 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 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 several tests.
- Radiology: X-rays of dogs with juvenile hyperparathyroidism show changes in the appearance of the bones due to a decrease in bone density.
- Baseline blood tests: Basic blood tests often reveal changes in calcium or phosphorus, which raises the suspicion of hyperparathyroidism. 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, they 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. If your dog has an abnormally high level of parathyroid hormone in the blood, it 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; one to three of these glands are removed to bring calcium levels into a more normal range. Multiple surgeries may be required to achieve the correct calcium balance. With surgery, the prognosis for this condition is typically good.
