Hyperthyroidism in Cats

What is Hyperthyroid Disease?

Hyperthyroid disease, also called hyperthyroidism, is a common disease in cats 8 years and older. The thyroid glands normally work to maintain and regulate metabolism. When the thyroid glands begin producing more than normal amounts of thyroid hormones, this increases a cat’s metabolism, resulting in weight loss despite an increased and sometimes ravenous appetite.

By staying aware of your cat’s everyday habits and behaviors as well as regular veterinary visits, hyperthyroid disease can be detected early and managed appropriately with the help of your vet.

Signs of Hyperthyroid Disease in Cats

Cats are masters at hiding disease. Be alert to the following subtle signs or changes in your cat that may indicate hyperthyroidism:

• Ravenous appetite
• Weight loss
• Vomiting
• Diarrhea
• Increased drinking and increased urination
• Behavioral changes such as urinating or having bowel movements outside the litterbox
• Other behavioral changes such as overactivity, aggression, or vocalize (meow) more often
• Hiding/sleeping in unusual places
• Dull, dry, flaky, and/or matted fur, not grooming as usual

Hyperthyroidism affects the heart, causing an increased heart rate and sometimes a heart murmur. If left untreated, this can result in heart enlargement, heart failure, and death. Due to the effects on the heart, cats can also develop high blood pressure (hypertension). If not managed properly, hypertension can cause damage to the vessels in the eyes and lead to blindness.

Diagnosing Hyperthyroidism in Cats

Your vet will begin by asking you for a detailed history of your cat’s signs and symptoms including litter box habits, weight changes, eating and drinking habits and amounts, activity levels, and changes in behavior/moods. After a thorough physical exam, diagnostic tests such as blood work, x-rays or ultrasound, and urinalysis will be recommended to determine a diagnosis.

Specific Testing:

Your vet will recommend a blood test to evaluated thyroid hormone levels circulating in your cat’s blood. A senior cat blood test is also recommended to provide additional information about the internal organs such as kidneys, liver, and more. These tests allow your vet to determine the best way to manage and treat your cat’s illness.

Senior cat blood work also typically includes a complete blood cell count, urinalysis, and testing for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV). X-rays and/or ultrasound examinations and blood pressure testing are recommended to assess the heart, kidneys, and other organs that can be affected by hyperthyroidism.

While these diseases occur independently of each other, chronic kidney disease (CKD) and hyperthyroidism both tend to occur in older cats. With overlapping symptoms, CKD and hyperthyroidism are often diagnosed at the same time. You can read more about kidney disease in cats here!

Treatment and Management of Hyperthyroidism in Cats

There are 4 options for the treatment of hyperthyroidism in cats. Each option has advantages and disadvantages. The best treatment for your cat must be determined by you, your vet, and your cat’s health status based on lab work results and lifestyle. Management strategies may change over time, based on your cat’s response to the treatment.

1. Strict, special prescription diet prescribed by your veterinarian

2. Daily medication (usually given every 12 hours lifelong)

3. Surgery (to remove all or part of the thyroid gland)

4. Radioactive iodine treatment

Note that hyperthyroidism is a lifelong condition. If left untreated, it can cause increasingly serious symptoms and may eventually lead to a painful death. However, successful treatment and continued veterinary management allow many cats to return to normal with a positive long-term outlook for a normal, healthy, active life.

Can hyperthyroidism be prevented?

Hyperthyroidism may be caused or worsened by long-term consumption of canned cat foods, especially from pop-top cans and/or liver and giblets flavors. Cats diagnosed with hyperthyroidism or early disease may benefit from changing to food that isn’t from a pop-top can and not liver and giblets flavored. Make sure to talk to your vet before changing diets if your cat is showing signs of hyperthyroidism.

Read more:

Arthritis in Cats

Diabetes in Cats

Why is my cat not eating? 3 Common Causes of Anorexia in Cats

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