SPCA New Zealand
Advice & welfare

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How do I diagnose and treat hyperthyroidism in cats?

My friend’s cat was recently diagnosed with hyperthyroidism and I am worried that my cat Tarzan may have the same problem. How would I know and, if he does have it, can it be treated?

Hyperthyroidism is a very common disorder of older cats, in which their thyroid glands become overactive and produce excessive amounts of thyroid hormones. These hormones help control the body’s metabolic rate and are also involved in the regulation of many body processes. Too much of the thyroid hormones can cause cats to become very ill. Cats with hyperthyroidism tend to lose weight despite having an increased appetite and eating more food. They often also have increased thirst and drink more; increased activity, restlessness or irritability; an increased heart rate; and a poor and scruffy looking hair coat. Some cats get diarrhoea and/or vomiting, and some may pant when they are stressed (which is unusual in cats). Occasionally a cat with hyperthyroidism will show non-typical clinical signs such as generalised weakness, lethargy, and loss of appetite but this is far less common.

If Tarzan is showing signs such as those described above you should take him to your veterinarian. Based on the clinical signs and a physical examination your veterinarian will likely be able to tell you if he or she suspects that Tarzan might be hyperthyroid. A blood test to measure the level of thyroid hormones will be needed to confirm the diagnosis. Sometimes additional tests may be needed.

Other tests will likely be performed at the same time to assess other potential concurrent problems (such as kidney disease); there are often abnormalities in other laboratory tests in hyperthyroid cats (particularly an increase in liver enzymes is common). Your veterinarian will be able to advise you on what these mean and whether further investigation is needed.

It is really important that cats with hyperthyroidism are diagnosed and treated appropriately. When hyperthyroidism is uncontrolled it can have important negative consequences in the body including damage to the heart (eventually causing heart failure if untreated) and high blood pressure (which can damage organs such as the eyes, kidneys, heart, and brain).

The good news is that the majority of cats that develop hyperthyroidism can be treated very successfully and make a complete recovery, with complete reversal of all the signs of hyperthyroidism. There are a number of different options available including medical management with anti-thyroid drugs, surgery to remove the overactive thyroid gland, dietary therapy, and radioactive iodine therapy. Each option has its pros and cons and your veterinarian will be able to advise you which is the best option for your cat and circumstances.

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