Senior Cats at Risk for Hyperthyroidism

[Dr. Gary Brummet examines a cat]

Prognosis Is Good with Early Diagnosis

Senior cats are at a greater risk for developing hyperthyroidism than any other age group of cats. In fact, 95% of cats with hyperthyroid disease are 10 years old or older. Dr. Gary Brummet, the small animal primary care veterinarian at the University of Illinois Veterinary Teaching Hospital in Urbana, sees several of these cases each year.

Hyperthyroidism is a disease in which there is an overproduction of thyroid hormone in the body. Thyroid hormone regulates the body’s metabolism, heart rate, and digestive function. When the hormone level becomes excessive, some life-threatening symptoms may occur.

Hyperthyroidism Signs

“Typical signs of hyperthyroidism in cats include rapid weight loss, rapid heart rate, and increased hunger,” Dr. Brummet says.

It is typical for older cats to lose weight as they age, making it hard to distinguish hyperthyroidism from normal aging. If left undiagnosed, hyperthyroidism may cause eye problems. Dr. Brummet takes into account the cat’s history and other symptoms for a proper diagnosis. Some less common symptoms he sees are an increase in meowing and behavioral changes.

It is common for a veterinarian to perform a bloodwork panel on senior cats during their clinic visit. The thyroid hormone levels are tested in this panel to detect any abnormalities. Abnormal thyroid hormone levels cause an increase in blood pressure.

“Most cases of hyperthyroidism are caught in the early stage because the owners notice the changes in their cat and seek the help of their veterinarian right away,” Dr. Brummet says. A treatment plan is tailored to the needs of the patient.

“Hyperthyroidism has no cure. Instead, the goal of treatment is to control the disease and allow the cat to feel better,” says Dr. Brummet. It is important to decrease high blood pressure so that the other issues that accompany this will also subside. There are four types of treatment available for hyperthyroidism.

Hyperthyroidism Treatment Options

“The first treatment option is an oral medication called methimazole,” Dr. Brummet says. Using this treatment lowers the cat’s excessive thyroid hormone (T4) production to a normal level. This treatment plan requires monitoring the kidneys to ensure further disease processes aren’t happening.

If medical treatment is not effective for the cat, then surgery or a radioactive treatment option may be considered. These methods are rarely used. Surgery removes the thyroid gland from the animal entirely, thus stopping production of the thyroid hormone. The radioactive agent used is done only in specialty clinics equipped to handle such material and these patients. The University Illinois Veterinary Teaching Hospital is able to perform this. A complete list of clinics where this is done can be found at, which is a private company.

“A newer treatment option for hyperthyroidism in cats is a prescription diet called Hill’s Y/D,” says Dr. Brummet. Y/D diet is low in iodine, which is a precursor to the thyroid hormone that is causing the problem. Dr. Brummet recommends the diet in combination with the oral medication upon diagnosis to help get the patient’s hyperthyroidism under control.

Communication with Veterinarian Is Key

Prognosis for cats with hyperthyroidism is usually pretty good, provided that the disease was diagnosed and treated early on. Hyperthyroid cats can live a normal, healthy life well into their senior years!

At this time, there are no known preventive measures for feline hyperthyroidism. Dr. Brummet strongly advises that owners note any changes that a cat may be experiencing, whether related to health issues or to behavior, and discussing these changes with the veterinarian right away.

Owners of cats with hyperthyroidism should stay in close communication with their veterinarian and should make sure their pet is getting prescribed medication or treatments and is being rechecked by the veterinarian regularly.

If you have any questions about hyperthyroidism in cats, contact your local veterinarian.

By Beth Mueller