Hyperthyroidism in Cats: A Cat Owner’s Guide

Feline hyperthyroidism is a common hormone-related (endocrine) disorder that involves an overactive thyroid in cats. It typically affects middle-aged and older cats, especially those over 10 years old, and is diagnosed in up to 10% of senior cats in the United States.¹

Read on to learn more about what is hyperthyroidism in cats, how to treat hyperthyroidism in cats, and how to prevent hyperthyroidism in cats if possible.

What is Cat Hyperthyroidism?

The thyroid gland is a small, butterfly-shaped organ located in your cat’s neck, near the windpipe. It produces thyroid hormones, mainly T₄ and T₃, which help regulate many important body functions, including metabolism, heart rate, body temperature and digestion.

Of thyroid problems in cats, this particular condition is caused by the overproduction of thyroid hormones T₄ and T₃, most often due to a noncancerous enlargement of one or both thyroid glands. In rare cases (less than 3%), it may be due to thyroid cancer.¹ Hypothyroidism in cats, on the other hand, involves an underactive thyroid, and is not often naturally seen.

Symptoms of Hyperthyroidism in Cats

Feline hyperthyroidism can affect many parts of your cat’s body, and hyperactive thyroid symptoms in cats often appear gradually. Recognizing early changes in behavior or health can help you catch the condition sooner and get your cat the care they need. If you have any questions or concerns about your cat’s symptoms, reach out to your veterinarian; they are the best resource to help you decide what steps to take next.

Classic Signs of Hyperthyroidism

Hyperthyroidism typically affects cats over 10 years of age. Many cats with hyperthyroidism seem unusually energetic, have a strong or even increased appetite, yet continue to lose weight. Some may start drinking more water, often from unusual places like dripping faucets or plant containers.

It could be a sign of hyperthyroidism if you’ve found yourself thinking any of the following¹:

• “My cat seems confused or not quite herself.”
• “He’s always hungry, no matter how much I feed him.”
• “She’s acting like a kitten again, full of energy.”
• “I can’t believe how young and active my 16-year-old cat is.”
• “He must be losing weight from all the extra exercise.”
• “I thought the diet was finally working.”

Common Signs to Watch For

Cat hyperthyroidism symptoms include:

• Noticeable, unplanned weight loss, even with a good or increased appetite
• Drinking and urinating more than usual
• Increased energy or restlessness, sometimes with more vocalizing
• Fast breathing or a rapid heart rate
• Vomiting or diarrhea
• A messy or unkempt haircoat
• Muscle loss, especially along the spine and back legs
• A lump in the neck that may be an enlarged thyroid gland
• Reduced appetite, low energy or seeming withdrawn in some cats with more advanced disease

Early Signs

Signs of hyperthyroidism in cats that may be noticeable early on include:

• Subtle, unplanned weight loss
• Slight changes in energy or behavior
• Mild increase in thirst or appetite

When to See the Veterinarian

If your cat is over 10 years old and showing any of these cat thyroid symptoms, schedule a veterinary visit. Your veterinarian may recommend blood tests to check thyroid hormone levels. Routine checkups and lab work can catch hyperthyroidism in cats (and other cat thyroid issues) early and help manage it before it causes serious health issues.

Causes of Hyperthyroidism in Cats

Hyperthyroidism is one of the most common diseases seen in older cats. But what exactly causes thyroid disease in cats? While there is no single answer, researchers believe the condition develops because of a combination of factors, listed here. Understanding these factors can help you be proactive about your cat’s health.

How to Confirm Cat Thyroid Problems: Veterinary Diagnosis¹

If your veterinarian suspects hyperthyroidism, they will start with a full physical exam. This includes checking your cat’s weight, heart rate, breathing and the neck area for an enlarged thyroid gland. Your veterinarian will also listen for heart murmurs or irregular rhythms and assess coat quality, which may appear rough or poorly groomed. An eye exam may be done to look for signs of high blood pressure that can affect the eyes. However, a definitive diagnosis requires a blood test. Please see this article for more information on tests used to diagnose hyperthyroidism.

Treatment for Hyperthyroidism in Cats¹

Once your cat is diagnosed with hyperthyroidism, the next step is choosing the best treatment. The goal is to bring thyroid hormone levels back to normal while protecting the kidneys and overall health. Before starting, your veterinarian will often recommend checking kidney function, blood pressure and urine protein to help determine the safest option.

Outlook for Cats With Hyperthyroidism

With proper treatment, most cats with hyperthyroidism live long, healthy lives. Thanks to better awareness, routine screening and effective treatment options, early detection greatly improves outcomes.

For more expert tips, explore the causes and diagnosis as well as the treatment of hyperthyroidism in cats.

Reference

1. Carney HC, Ward CR, Bailey SJ, et al. 2016 AAFP guidelines for the management of feline hyperthyroidism. J Feline Med Surg. 2016;18(5):400-416.