Feline Hyperthyroidism

The thyroid gland is located in the neck and plays a very important role in regulating the body’s rate of metabolism. Hyperthyroidism is a common disorder in cats older than eight years of age. The disease is caused by an enlargement of the gland, which leads to an overproduction of thyroid hormone.

Many organs are affected by this disease, including the heart, kidneys, liver, and eyes (retinas). The most consistent finding with this disorder is weight loss secondary to the increased rate of metabolism. In fact, some of these cats have a ravenous appetite. Affected cats may also drink a lot of water, urinate frequently, vomit, or have an unkempt hair coat. In addition, high blood pressure and heart disease are secondary complications of this disease.

In most instances, a diagnosis of this disease can be made with the aide of blood testing and palpation of an enlarged thyroid gland. In addition, the overall health of the cat must be evaluated. An EKG, blood tests, urinalysis, x-rays, blood pressure determination, and cardiac ultrasound can be performed.

There are three treatment choices; any one of them could be the best choice in certain situations.

1. Radioactive Iodine Therapy - the iodine is given by injection and destroys all abnormal thyroid tissue without endangering other organs. Treatment requires one or two weeks of hospitalization at a veterinary hospital licensed to administer radiation therapy.

2. Surgery – Surgical removal of the affected thyroid lobe(s) is also very effective. Because hyperthyroid cats are usually over eight years of age, there is a degree of risk involved. However, if the cat is otherwise healthy, the risk is minimal. Removal of both glands is recommended due to the likely recurrence of disease in the unremoved gland.

3. Oral medication – Administration of an oral drug, methimazole (tapazole), can control the effects of the overactive thyroid gland. Some cats have reactions to the drug, and can include vomiting, lethargy, anorexia, fever, and anemia. Methimazole does not destroy the abnormal thyroid tissue but rather prevents the production of excess thyroid hormone. Therefore, the drug must be given for the remainder of the cat’s life. This type of treatment is appropriate for the cat that is a poor surgical risk due to other health problems.

Many owners of cats with hyperthyroidism are hesitant to have radiation therapy or surgery because of their cat’s advanced age. But, remember, old age is not a disease. The outcomes following both surgery and radiation therapy are usually excellent, and most cats have a very good chance of returning to a normal state of health.

For more information, contact New Carrollton Veterinary Hospital at (301) 552-3800.

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