Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Feline Hyperthyroidism: A Common but Curable Problem


Pet Column for the week of October 27, 2003


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ann Marie Falk
Information Specialist

Feline hyperthyroidism is the most common hormonal disease diagnosed in cats today. It is arises when a tumor on the thyroid gland causes an increase in the secretion of thyroid hormones. Most often, the tumor is benign.

"For the past 20 years researchers have been searching for a cause, but the underlying cause of feline hyperthyroidism is not known. We do not know of any predisposing factors. Things such as food, vaccination status, and kitty litter do not put cats at risk for this disease," explains Dr. Thomas Graves, a veterinarian specializing in internal medicine at the University of Illinois Teaching Hospital in Urbana.

Feline hyperthyroidism is a disease seen more commonly in older cats. The average age of onset is 12 years. However, all cats over 8 years should be routinely screened. Early diagnosis is the key to successful treatment.

"Old age is not a disease! A skinny, scruffy cat does not look that way because it's old but rather because it has an underlying disease. Cats are very good at hiding disease until they are really sick," says Dr. Graves. "In the case of feline hyperthyroidism, lack of treatment can lead to an increase in blood pressure resulting in changes in the heart and kidney failure. Eventually death can occur due to congestive heart failure."

Cats with feline hyperthyroidism frequently have an increased appetite with concurrent weight loss and vomiting. They may also experience hyperexcitability and other behavioral changes. Some, however, show no signs of disease.

Because feline hyperthyroidism can look like chronic renal failure, diabetes, inflammatory bowel disease, and intestinal lymphoma, thorough diagnostics, including a urinalysis, complete blood work, and a chemistry panel, are necessary. An elevated concentration of the thyroid hormone in the blood points toward feline hyperthyroidism.

Currently there are three treatment options available: medical therapy, surgery, and radioiodine. Radioiodine is arguably the safest and most effective way to treat feline hyperthyroidism. One dose of radioiodine is given in a licensed nuclear medicine facility and a hospital stay of about 5 days is required.

Surgery is also usually curative, often less expensive, and can be done in many veterinary practices. In the hands of an experienced surgeon it is a safe procedure. No muscles need to be cut and no body cavities are opened, so post-surgical recovery is usually quick and uneventful.

"Feline hyperthyroidism can be managed medically with a drug called Tapazole. This medication is not curative and will need to be given for the rest of the cat's life. It works to control the hormone levels," explains Dr. Graves.

Tapazole is the cheapest form of treatment in the short term. There can be side effects from the drug, so cats will need to be monitored closely. Blood work should be checked every 2 to 3 weeks when starting up treatment.

Treating this disease can be very rewarding for the veterinarian, owner, and most importantly your cat!

If you have questions about feline hyperthyroidism, please contact your local veterinarian for more information.