Hyperthyroidism is a common disease of middle age or older cats. It occurs when the levels of thyroid hormone, produced by the thyroid glands in the neck, starts to rise.

Thyroid hormones are involved in regulation of the body’s metabolism. Classic signs of hyperthyroidism include increased appetite linked to unexpected weight loss and increased activity levels or restlessness. There can also be an increase in thirst. Other signs can include an unkempt and greasy coat. Occasionally vomiting and diarrhoea are seen.

On examination, affected cats often have increased heart rates and an enlarged thyroid gland, which will raise the vet’s suspicion. A blood sample to measure thyroid hormone levels is required to confirm the diagnosis as these signs can also been seen with other diseases. It is also important to check for other diseases which can be present at the same time such as kidney disease, liver disease and diabetes.

Treatment is always recommended, as uncontrolled hyperthyroidism can lead to other complications. The most damaging are heart disease (and potentially heart failure) and hypertension (high blood pressure), which, if left untreated, can cause damage to the eyes (including sudden blindness), heart, kidneys and brain.

Medication is recommended for initial stabilisation. Once the thyroid levels are stable there are four main options for longer-term treatment, which can be curative. The initial medication comes in the form of tablets, liquid or a gel. Long term treatment options include surgery to remove the affected gland(s), radioactive iodine treatment or in some cases a special diet. Frequently the medical treatment is so simple and successful the owners opt to continue this long-term.

Monitoring the response to treatment is important, especially during the initial stabilisation period but also for long term medical management. This ensures is to ensure that the thyroid hormone levels are correct, to monitor kidney function (as sometimes controlling hyperthyroidism can unmask pre-existing kidney problems) and to check for any side effects of treatment.

Most cats that are diagnosed with hyperthyroidism can be treated very successfully and go on to lead normal lives. In the majority of cases treatment can be very rewarding as a cat that was distressed and losing condition becomes more contented and clearly more healthy.