How to Treat Hyperthyroidism in Cats

Calico and white cat lying on a deck.
Hyperthyroidism is more common in older cats.

Getty Images/krblokhin

No one wants their cat to get sick but some illnesses can be easily managed with proper treatment. Hyperthyroidism is one such disease and is fairly common in older cats. By knowing the common symptoms of this disease, you can get your cat the veterinary attention that is needed to treat and manage it before other serious problems develop.

What Is Hyperthyroidism?

Hyperthyroidism, the opposite of hypothyroidism, is also known as thyrotoxicosis and occurs when the thyroid gland becomes enlarged and produces extra hormones. The thyroid gland is located in the neck and makes hormones called T3 and T4, which play a role in a variety of bodily functions, including metabolism and body temperature regulation. When a cat develops hyperthyroidism, too much T3 and T4 are produced causing a cat to become increasingly sick over time.

Symptoms of Hyperthyroidism in Cats

Symptoms of Hyperthyroidism in Cats

  • Excessive hunger
  • Weight loss
  • Increased thirst
  • Increased urination
  • Vomiting
  • Behavior Changes
  • Unkempt fur

The classic signs of hyperthyroidism are excessive appetite coupled with weight loss. Some cat owners say their cat seems to eat anything that isn't nailed down but somehow doesn't gain any weight. Instead, hyperthyroid cats lose weight and may also begin to drink and urinate more. Other common symptoms include vomiting, matted unkempt fur, and behavior changes like aggression and hyperactivity. 

Causes of Hyperthyroidism in Cats

There are two types of tumors that cause hyperthyroidism in cats. Most cases of hyperthyroidism are due to a benign tumor called an adenoma but in rare cases, a cancerous tumor called an adenocarcinoma is the cause. Both tumors cause the thyroid gland to become enlarged but no one knows what causes either type of tumor to grow to begin with.

Diagnosing Hyperthyroidism in Cats

If your cat is showing symptoms of hyperthyroidism, a visit to their veterinarian is warranted. The vet will perform a physical examination and obtain your cat's history before recommending blood screening be performed. Sometimes, enlarged thyroid glands can be detected during the physical exam. The blood screening will look at how well your cat's organs are functioning as well as measure how much thyroid hormone is being produced by your cat's thyroid glands. If these hormone levels are high, your cat will be diagnosed with hyperthyroidism. Other tests may be recommended as well to look for common complications seen with hyperthyroidism, like high blood pressure. 

Treatment of Hyperthyroidism in Cats

There are four ways to treat a cat that has been diagnosed with hyperthyroidism: dietary treatment, surgery, medication, and radioactive iodine therapy. Each option has its pros and cons and may not be right for every cat but the majority of cat owners opt to treat the disease with either diet or medication. Medications reduce the amount of thyroid hormones that the thyroid glands produce and the special diet restricts the amount of iodine a cat consumes. Iodine is essential for thyroid hormone production, so limiting iodine intake limits thyroid hormone production.

Radioactive iodine is often recommended as the ideal treatment option, if your cat is a candidate, and destroys the abnormal thyroid tissue. This procedure is not performed by every vet and can be costly but typically cures the disease so no further treatment is necessary. Surgery can also cure the disease but is more invasive than the other three options so it is not as commonly recommended.

How to Prevent Hyperthyroidism in Cats

Because no one knows what causes a cat to develop the tumors that cause hyperthyroidism, there is no way to prevent the disease. The best thing you can do as a cat owner is to address any symptoms of hyperthyroidism as soon as you see them. Additionally, treating the disease promptly upon diagnosis will help prevent other problems from developing. Regular check-ups and blood screenings for your older cat can help find a problem before it becomes serious so your veterinarian plays an important role in the long-term health of your cat.

Risk Factors for Hyperthyroidism in Cats

While no specific cat breed has a definitively higher risk for developing hyperthyroidism than another, any cat senior is at a greater risk for the disease. Some studies suggest that cats that eat mostly canned food, especially fish-based canned food, are at increased risk. One study showed that longhaired, non-purebred cats have a higher risk of developing the disease while Siamese, Burmese, Tonkinese, Persians, Abyssinians, and British shorthairs have a decreased risk when compared to domestic shorthairs.

More information is needed to continue to help cat owners and hopefully one day be able to prevent hyperthyroidism in all cats.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
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  1. Crossley VJ, Debnath A, Chang YM, Fowkes RC, Elliott J, Syme HM. Breed, Coat Color, and Hair Length as Risk Factors for Hyperthyroidism in Cats. J Vet Intern Med. 2017;31(4):1028-1034. doi:10.1111/jvim.14737