Excess levels of parathyroid hormone results in too much calcium in the bloodstream, which causes hypercalcemia. Excess amounts of calcium can lead to problems in the gastrointestinal, nervous and renal systems.

Hyperparathyroidism is an endocrine disorder that occurs when the parathyroid glands secrete excess amounts of parathyroid hormone. There are four small parathyroid glands located next to the thyroid gland in the cat's neck. When one or more of the parathyroid glands becomes overactive, it produces excessive amounts of the parathyroid hormone, which is responsible for regulating the correct balance of phosphorous and calcium in the blood. When blood calcium levels drop too low, the parathyroid hormone level increases, which allows calcium to be taken out of the bones to maintain the correct levels.

Symptoms may not be present until the blood calcium levels have been at an increased level for a sustained period of time. These symptoms include:

There are two types of hyperparathyroidism:

Primary hyperparathyroidism is caused by one or more benign tumors, which are known as adenomas, that are located on the parathyroid gland. The tumor causes the parathyroid to secrete excess parathyroid hormone. Malignant parathyroid tumors are extremely rare in cats.

Secondary hyperparathyroidism is caused by a nutritional problem or other disorders. Causes of secondary hyperparathyroidism include:

The veterinarian will need the cat's complete medical history, an approximate date when the symptoms began and a detailed list of all of the symptoms. The veterinarian will physically examine the cat, which will include feeling for an enlargement of the parathyroid gland, looking for muscle and gait abnormalities, and listening to the cat's breathing and heart rate.

Labs, which will include a complete blood count, biochemical profile, and a urinalysis, will be performed. These labs will show the calcium and phosphate levels in the blood and urine and if kidney disease is present. Elevated levels will confirm the diagnosis of hyperparathyroidism. Additional tests will then be performed in order to determine if a tumor or a nutritional deficiency is the cause. An ultrasound and X-ray will be performed to look at the thyroid and parathyroid glands. These tests will look for the presence of a tumor. Other blood tests may be performed to determine what nutritional deficiencies are present.

Because the parathyroid gland is so small, exploratory surgery may be necessary to find the tumor and determine the cause of the hyperparathyroidism.

Primary hyperparathyroidism is treated by removing the gland that is causing the elevated hormone secretion; surgery is one of two options for removal. The cat will need to fast prior to the surgery. General anesthesia will be administered before the veterinarian makes a small incision on the underside of the cat's neck, allowing for the exposure and removal of the gland.

Alcohol or heat treatment is the second option for removing parathyroid glands with tumors. These procedures are less invasive than surgery. Alcohol treatment has a 90 percent success rate while heat treatment has a 50 percent success rate. Using an ultrasound for guidance, a needle will be inserted into the gland. Alcohol or heat will be administered in an attempt to destroy the gland, which will cause the excess secretions to cease. Both surgery and alcohol or heat treatments require hospitalization. Because of the sudden drop in secreted parathyroid hormones, the cat's calcium levels will be closely monitored. Calcium supplements may be necessary until the body properly regulates itself.

Secondary hyperparathyroidism will be treated by correcting the nutritional deficiencies that caused the excess levels to occur. The veterinarian will prescribe a special diet for the cat and may prescribe additional supplements to correct these deficiencies.

Cats who present with hyperparathyroidism due to chronic kidney disease will need to receive treatment for their kidney problems. This may include medications and being placed on a low-phosphorous diet.

The cat will need to follow up with the veterinarian to continue to monitor its calcium and phosphorous levels under they are regulated. Cats who receive alcohol or heat treatment will need additional ultrasounds and tests to determine if the gland was successfully destroyed. If the treatments were not successful, surgery will be necessary. Cats with chronic kidney disease will also need to follow up with the veterinarian to have their kidney function monitored on a regular basis. With proper treatment, cats with hyperparathyroidism have a good prognosis.