If your cat drinks a lot of water, seems constantly hungry, yet never puts on any weight, it might have a problem with its thyroid gland. A cat gets feline hyperthyroidism when the thyroid starts over-producing the hormones which regulate the body's metabolic rate and therefore the overall activity of the cat.

If it is not treated, hyperthyroidism in cats often results in heart failure. But the good thing is that in most cases treatment is both possible and straightforward.

Hyperthyroidism is uncommon in cats under 10 years old but may affect as many as 2% of cats older then this. The average age at which a cat might get hyperthyroidism is about 13.

How do I know that my cat may suffer from hyperthyroidism?

Not all cats with hyperthyroidism lose weight, though almost all will start eating and drinking noticeably more. You will notice an increased insistence and frequency in demands for food, but the overeating will often result in vomiting and diarrhea. The cat drinking more water and urinating often is also a good indicator that there might be a problem. Cats may become more noisier and more energetic. When the cats are brought to the vet, people often comment that there can not be much wrong with their pet since she is so lively and eating well. However, good appetite is one thing - overeating is another matter. If your cat does start to eat noticeably more than normal or shows any of the other symptoms described here, head for the vet. If your cat is elderly, go sooner rather than later. The vet will have no trouble diagnosing whether or not the cat has hyperthyroidism. The condition generally causes an enlarged thyroid which can be felt as a hard lump under the skin. The vet will easily check this with a physical examination which can be confirmed by a blood sample which checks for thyroid hormones in the blood. A high thyroxine (T4) concentration (the main hormone) is usually all that is required for the diagnosis in most cases.

Secondary complications caused by hyperthyroidism

Because thyroid hormones affect the function of almost all organs, hyperthyroidism may cause other parts of the body to malfunction, and this will need to be treated separately. Such problems are particularly common if the illness is not caught and treated early. One of the common complications is problems with the cat's heart. The thyroid hormones stimulate the heart to beat faster and the heart muscle to contract more strongly. If the hyperthyroidism is not treated, the muscle of the largest chamber in the heart (the left ventricle) enlarges and thickens - so called 'left ventricular hypertrophy'. If nothing is done about this, it will eventually result in heart malfunction. Hypertension (high blood pressure) is another potential complication which can cause additional damage to several organs including the eyes, kidneys, heart and brain.


There are three main treatments for hyperthyroidism: drug treatment, surgery and radioactive iodine therapy. The choice of treatment will be determined by the underlying cause of the problem and usually also by the costs involved. Drug treatment involves giving the cat pills twice a day. This is a low cost non-invasive method which avoids general anaesthesia. However, apart from the issues involved with getting pills into cats, some cats may get side-effects which normally include vomiting. Also if hyperthyroidism is caused by cancer, the pills do not eliminate the underlying cause. In such cases, especially with a fast-growing cancer, surgery may be the option to go for, despite the fact that with surgery there are always risks involved. If the cancer has spread, surgery may not remove all of it. Alternatively, radioactive iodine provides a safe and effective treatment for hyperthyroidism. Like the surgery, it is cures, rather than treats the condition, but despite the scary name, radioactive iodine is much safer. The iodine is injected under the skin and then taken up by active thyroid cells. Because the cancerous cells are most active, they take up most of the radioactive material. This kills those cells but does not damage surrounding tissue. There are also fewer side-effects than with drugs or surgery. The only problem with radioactive iodine therapy is that it has to be carried out in a hospital under protective conditions, and the cat has to remain in the hospital until the radioactive level falls down and does not pose any risk to people handling the animal. As a result this treatment can get costly. However, the success rate after a single treatment is 95% and it can be repeated if necessary. Normally after iodine treatment thyroid hormones are restored to normal levels within three weeks.

Note: This information is for guidance only. It is not intended to replace consultation with a licensed practitioner.

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