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Hyperthyroidism In Senior Cats

Hyperthyroidism In Senior Cats
by Dr Grant Hampson

Read time: 3 min

Has your cat recently been diagnosed with hyperthyroidism? Or are you worried they might have developed it?

We're here to help. In this article we'll explain what hyperthyroidism is, how your cat might get it, how it's diagnosed, and how you can help your cat manage their symptoms.

The thyroid glands are two small organs found under the skin in the neck. Thyroid hormone is produced here and is heavily involved in a cats metabolism. Your cat’s body works hard regulating their hormones but in some cases the thyroid gland can become overactive, producing too much of the thyroid hormone. The cause of this overactivity appears to be caused by a benign cancer, but we are still unsure of why this happens.

Illustration of a cat's thyroid showing a normal and an enlarged thyroid gland

The symptoms of hyperthyroidism are all associated with an increase in metabolism. The most noticeable symptom is a massive increase in their appetite, they can often be described as ravenous. Despite this increase in appetite your cat will lose weight at a dramatic weight. Other symptoms include drinking and urinating more than usual, vomiting and diarrhoea.

As well as the symptoms that you see, there may also be some changes inside the body. The heart starts to work extremely hard, beating much quicker. This extra work may cause the muscles of the heart to thicken which can result in symptoms of heart failure. Your cat’s blood pressure can also increase which can lead to multiple organ damage if left untreated for a long period of time.

Fortunately, hyperthyroidism can be successfully treated and there are multiple options available:

Medicine - there are medications available that stop the production of the thyroid hormone. The medication is often very effective but it is important to remember that it is life-long therapy, and medication is given one to three times a day, depending of the medication selected.

Surgery - The surgery involves removing the diseased gland. Having the surgery means there is no longer need for daily, life-ling medications. The surgical option is not suitable for all cats and there are a couple of things to consider before going down the surgical route:

  • Your cat will need a general anaesthetic, which always carries a slight risk.

  • They may need medication for a few weeks prior to the surgery to stabilise their condition first.

  • They may need a second surgery in the future if the other thyroid gland becomes overactive.

  • Multiple vet checks are needed following the surgery to monitor the calcium levels.

Radiation - This is known as “radioactive iodine therapy” and is targeted to destroy the overactive thyroid tissue whilst reserving the healthy cells. This is achieved through injections and has few side effects. 9 out of 10 cats are cured in their first course of therapy. For this treatment option your cat will need to stay in hospital for a reasonable period of time to allow the radiation levels to drop before coming home, which can be around 4 weeks.

All the treatment options have advantages and disadvantages. There are lots of this to take into consideration before selecting which to go for, and you should always discuss this in detail with your vet. Hyperthyroidism is a serious disease but is easily treated and in some cases cured.

If you have any questions about hyperthyroidism, or want to know more about how you can help your cat, contact us at

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