What You Ought to Know About Thyroid Problems in Cats

Usually hyperthyroidism presents with a skinny, hyperactive old cat with a ravenous appetite. But sometimes it’s quite the opposite.

Thyroid problems in cats
Thyroid problems in cats: Wembly was diagnosed with hyperthyroidism.

An overproduction of thyroid hormone (hyperthyroidism) is the most common hormonal disparity experienced in cats. While hyperthyroidism can develop in cats as young as 4, it is more common in older cats, especially those around 12 or 13.

Feline thyroid problems are believed to stem from environmental, nutritional and immunological factors, all of which play a role in developing tumors. The tumors, in turn, stimulate the glands to produce increased thyroid hormone. There are no known genetic tendencies for hyperthyroidism.

According to Clinical Endocrinology of Dogs and Cats, all felines are possible candidates for getting the condition, regardless of breed or gender.


Symptoms of Thyroid Problems in Cats

The symptoms of this condition vary widely. It is unusual for a mass to be noticeable to the naked eye, as the tumorous glands remain small. Many organ systems can be affected, which brings about the various symptoms.

More than half of affected cats experience weight loss, increased appetite, heart murmurs or raised heartrates. Other common symptoms of hyperthyroidism include vomiting, increased thirst and urination, and increased activeness. On the flip side, lack of appetite, little energy, respiratory problems or diarrhea can also be an alert to possible thyroid problems in cats.

A “classic scenario” of hyperthyroidism in felines would be a skinny, hyperactive old cat with a ravenous appetite as well as increased urination — a senior cat that looks very tense and has a low stress tolerance. But in about 10% of cases, that scenario would be quite the opposite: The cat might seem sluggish and have no appetite. The latter scenario represents the final stage of the disease (referred to as apathetic), and possibly signals cardiac disease as well.

Video Overview

Watch this quick video from Karen Becker, DVM, which offers a basic understanding of the illness. After the video, we’ll discuss treatment and prognosis.


Once your veterinarian suspects hyperthyroidism, she will check both of the thyroid lobes. Usually they will be enlarged. However, enlargement of the lobes does not necessarily mean that hyperthyroidism is the culprit; final diagnosis should depend on a direct measurement of thyroid function, involving blood testing. If the blood tests are not conclusive enough, a nuclear medicine scan of the thyroid glands may have to be performed.


There are three types of traditional medical treatments available for hyperthyroidism:

  1. Lifelong oral medication: Anti-thyroid drugs can be effective. But it is important that the feline is given the medication as long as she lives. Untreated, the condition can lead to congestive heart failure.
  2. Surgery: Surgical removal of the thyroid gland is best if only one gland is affected. Even then, a complication can occur if the remaining gland becomes successively hyperactive.
  3. Treatment with radioactive iodine: For this procedure, the cat will have to be hospitalized for several days, maybe even a few weeks, to allow the radioactive material to clear before the cat is handled by family members. Once your cat returns home, your veterinarian will advise you on precautions that will need to be taken to reduce your pet’s risks of having a toxic reaction to the radioactive treatment.

Mark Peterson, DVM, who spent more than three decades at Animal Medical Center in New York, hails the benefits of radioactive iodine in this video:

All of the available treatment options should be discussed with your veterinarian before deciding which option is best for your situation.

Long-term Outlook

In cats without severe cardiac problems, the prospects of returning to a healthy condition are excellent, although recurrence may show up over a period of time.

In ending, let me remind you that older cats with thyroid problems often also suffer from kidney disease. Strangely, hyperthyroidism can actually improve kidney function, so some cats with kidney disease may show a worsening kidney function after treatment for overactive thyroid glands. Discuss any kidney problems your cat may have with your veterinarian, as she may recommend monitoring the cat’s kidney functions.

Of course, this is just a general overview, and I am not in the business of dispensing medical advice. To learn more about thyroid problems in cats, strike up a conversation with your veterinarian, who is best equipped to advise you on your particular situation.

Additional Resources

  • Jeff S. Stortz, DVM, and five other vets: Feline hyperthyroidism article
  • Lorie Huston, DVM: Hyperthyroidism in cats
  • American Association of Feline Practitioners: Brochure on hyperthyroidism in cats

Photo: young and with it/Flickr


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