7 Things You Should Know About Hyperthyroidism in Cats

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You’ve noticed that your senior cat’s coat has been looking pretty matted lately. She’s eating like crazy, but still losing weight. Suddenly she’s hyper and crying at night, and when you go to clean the litter box, she’s full of urine. You know something is wrong, that it’s a health problem, so you take Fluffy to the vet. A blood test shows that he has hyperthyroidism. So what can you do about hyperthyroidism in cats?

First, you need to understand what you are dealing with. Here are some questions and answers to help you get started.


1. What are thyroid glands?

Cats with hyperthyroidism tend to look pretty scruffy. Photography by Suphaksorn Thongwongboot / Shutterstock.

The thyroid glands are two small parts located on either side of your cat’s windpipe (trachea). Their job is to produce hormones that affect many body functions. However, the most important thing in hyperthyroidism is to control the rate at which energy is burned in your cat’s body.

2. What happens in hyperthyroidism in cats?

A tumor grows on the thyroid gland and causes the body to produce too much thyroid hormone, which causes your cat’s body to burn energy too quickly.

3. What are the symptoms of hyperthyroidism in cats?

Because your cat’s body is burning energy too quickly, the first thing you will probably notice is that your cat is still hungry and losing weight despite massive food intake. She also drinks and urinates too much. Hyperthyroidism can lead to behavioral changes such as increased activity and restlessness, and sometimes even aggression. Your cat’s coat will begin to look greasy and unkempt.

4. How is hyperthyroidism diagnosed in cats?

Your veterinarian will perform a blood test to measure the levels of thyroid hormones in your cat’s blood. If the levels of these hormones are high, your cat is hyperthyroid.

5. What are the treatment options for hyperthyroidism in cats?

There are three common treatments for hyperthyroidism in cats: Medication, radioactive iodine therapy, and surgery. All three have risks and benefits.

Medication – usually methimazole (Tapazol) here in the United States – lowers the level of thyroid hormones in your cat’s blood. It is available in tablet or gel form that is applied to your cat’s skin. Most cats tolerate methimazole quite well. The drug seems to be the cheapest option, but in the long run the cost can add up.

Radioactive iodine (I-131) therapy is considered the gold standard of treatment, but you may have difficulty finding a clinic that offers it within a reasonable distance. It is quite expensive, but the good news is that your cat’s hyperthyroidism is cured after treatment.

Surgical removal of the thyroid gland is an option, but may not solve the problem. There may be tumor cells in other parts of your cat’s body that continue to overproduce thyroid hormones, or removal of the gland could mean that she no longer produces enough thyroid hormones and will need to take medication for the rest of her life.

6. What about prescription food for cats with hyperthyroidism?

This food is designed to be low in iodine, a chemical that helps the thyroid gland produce hormones. It is widely marketed to veterinarians and cat lovers, but there is considerable controversy among veterinarians I know about whether it has been adequately researched and what effects iodine deficiency can have on a cat’s overall health.

7. What complications can hyperthyroidism cause in cats?

Hyperthyroidism in cats can mask other diseases, such as kidney disease, because “running too hot” improves kidney function. Other possible complications include high blood pressure, heart problems and breathing difficulties.

Hyperthyroidism in cats is a disease that can be managed, but it requires your determination and good communication between you and your veterinarian.

Do you have a cat with hyperthyroidism? What treatments have you tried, and how have they worked for you? Are there any support groups you would recommend? Share your experiences in the comments.

Thumbnail: Photography by John E Heintz Jr. / Shutterstock.

By JaneA Kelley , September 23, 2019

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