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Cats with hyperthyroidism have a thyroid gland that is producing excessive amounts of thyroid hormones.
These hormones have several functions:
•they are essential to proper growth of body cells
•they help regulate metabolism of protein, fat and carbohydrate by cells
•they are involved in the regulation of heat production and oxygen consumption
This excessive amount of hormone causes a dramatic increase in the body’s metabolic rate – the speed at which the body uses up calories.
This means that a cat with hyperthyroidism burns calories very quickly and has to eat a lot of food to provide this energy. As the condition progresses it becomes increasingly difficult for a cat to eat enough to provide the huge amount of energy required, so they start to lose weight. This is why the most common clinical sign in cats with hyperthyroidism is weight loss despite a ravenous appetite. A high metabolic rate also causes increased heart rate, high blood pressure and restlessness. Cats may also have an increased frequency of vomiting and diarrhoea, increased drinking and an unkempt coat.
In 98% cases, the enlarged thyroid gland is benign – meaning non-cancerous. So far science still does not fully understand why some cats develop an overactive thyroid although it is age related with most hyperthyroid cats developing the disease from 12 years old onwards.
It is really important to diagnose and treat hyperthyroidism as left untreated your cat may develop secondary problems such as heart complaints and problems due to high blood pressure – such as damaged retinas in the eye (which can result in blindness) or kidney damage.
If you think your cat may have any of these symptoms, you should contact us immediately. Diagnosis is normally very straightforward. This will include the vet trying to feel an enlarged thyroid gland in your cat’s neck and taking a blood sample to measure thyroid hormones. We may also suggest that other blood tests are performed at the same time to assess other organ function, as other medical conditions might affect the successful treatment of hyperthyroidism. We ve already mentioned that increased blood pressure can affect kidney function so it is important we check for this problem as well as this may need additional treatment – see factsheet on kidney disease in the cat.
Hyperthyroidism can be treated very successfully. It is common for us to prescribe an initial period of tablets to help neutralise the excessive thyroid levels in order to stabilise the condition. Long term options include lifelong medication with tablets, surgical removal of the over-active gland or treatment with radioactive iodine to kill off the overactive portion of the gland. These options all have advantages and disadvantages and how appropriate they are for each individual cat and what suits you best as the owner will be discussed with your vet.
Long term, the outlook for your cat is good if we can maintain well managed hyperthyroidism.