Hyperthyroidism in cats
What is hyperthyroidism?
Hyperthyroidism is caused when the thyroid glands in your cat’s neck start over-producing thyroid hormone. In most cases, this happens because the glands have enlarged due to a benign growth called an ‘adenoma’.
Thyroid hormone is responsible for controlling your kitty’s metabolism and many of the signs associated with hyperthyroidism result from an increase in metabolic rate.
What are the signs of an overactive thyroid gland in cats?
- Weight loss
- Increased appetite
- Increased heart rate
- Hyperactivity or becoming more bad-tempered
- Becoming more vocal
- Unkempt or poor coat condition
- Increase in thirst
- Vomiting and diarrhoea
How will my vet diagnose an overactive thyroid?
First, your vet will talk through your pet’s signs and conduct a thorough examination. Your vet will check your pet from head to tail taking note of their weight and heart rate, and may palpate your pet’s neck to see if they can feel an enlarged thyroid gland. Typically, cats with hyperthyroidism are middle-aged to older with most being more than 8 years old. If your four-legged friend fits into this category and your vet thinks your kitty may have hyperthyroidism, blood tests are likely to be recommended.
Blood tests to check thyroid hormone (T4) levels are the only way to confirm the diagnosis. As well as checking thyroid hormone levels, blood tests will usually be run to screen for any other underlying disease, especially kidney or liver problems.
Many cats with an overactive thyroid will have high blood pressure so this is likely to be checked too.
How is hyperthyroidism treated?
The great thing about hyperthyroidism is that it can be quite successfully treated. So, what are the options?
Most cats with hyperthyroidism will start their treatment with anti-thyroid medication. This is available in tablet or liquid form and must be given once or twice daily. The medication decreases the production and release of thyroid hormone from the thyroid glands. It does not provide a cure so treatment will need to be continued for life, although your vet may discuss changing the treatment plan once your cat’s thyroid hormone levels have stabilised.
Anti-thyroid medication is readily available but can be difficult to administer depending on the patient! Talk to your vet if your kitty is tricky when it comes to taking medication; they may be able to advise you on how best to get your reluctant patient to cooperate! Alternatively, they may suggest other treatment options.
- Radioactive iodine treatment
Iodine is taken up by the thyroid gland and used to make thyroid hormone. Treatment with radioactive iodine is considered to be ‘gold standard’ for the management of cats with hyperthyroidism. The radioactive iodine is given by injection under the skin. It is rapidly absorbed and after being taken up by the thyroid, the radiation destroys the abnormal thyroid tissue.
Radioactive iodine provides a complete cure in 95% of cases, with thyroid hormone levels returning to normal within 1-2 weeks of treatment.
However, owing to the radioactive nature of the treatment, cats have to stay in hospital until their radiation levels have decreased to an acceptable level. Usually this will be 3 to 5 days after the injection.
Surgery to remove the enlarged thyroid glands (thyroidectomy) is generally very successful. Cats have two thyroid glands in their neck and in more than 70% of cases the disease will be bilateral; in other words, both glands will be affected.
Surgery will often provide a permanent cure, although occasionally signs will recur if thyroid tissue elsewhere in the cat’s body becomes enlarged. For example, many cats have small amounts of thyroid tissue in their chest.
- Dietary management
Iodine is essential for making thyroid hormone so feeding an iodine-deficient diet can help with the management of hyperthyroidism. They key to success is to ensure that cats whose hyperthyroidism is controlled in this way only eat their special low-iodine food, as even tiny amounts of iodine can make the diet ineffective. This can be a tricky task especially in those cats who like to explore outdoors.
The take-home message is that hyperthyroidism in cats can be successfully treated, and your kitty can be back to their fab feline self with a bit of help. If you have any concerns about your pet’s health, don’t hesitate to contact your vet.
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