One of the most common hormone diseases seen in older cats is hyperthyroidism, when the thyroid glands are over-active and produce an excessive amount of thyroid hormone. Thyroid hormone is a very important regulatory hormone in the body, playing a vital role in the regulation of metabolism, therefore when the amount of thyroid hormone in the blood stream is at an excessive level, the rate of metabolism is too fast.
This helps to explain the most common symptoms seen in cats with hyperthyroidism:
– weight loss
– hyperactivity or restlessness
– increased appetite (polyphagia)
– poor coat
– rapid heart rate (tachycardia)
An increased appetite hand in hand with weight loss is what most owners of hyperthyroid cats notice first, and is usually what makes an owner bring their cat to the vet for a check-up. Sometimes owners mistake the signs of hyperthyroidism as their cat just becoming old and frail. Some cats will also show some less common symptoms, including weakness and increased thirst. Hyperthyroidism is most commonly seen in cats older than 8 years of age. When an owner brings their cat to the surgery with symptoms that are consistent with hyperthyroidism, the Vet will take a full history and perform a thorough clinical examination. In cats with hyperthyroidism, it is very common at this stage to discover an enlargement of the thyroid glands in the neck (goitre), a rapid heart rate (tachycardia) and often some other changes which indicate high blood pressure (hypertension). A diagnosis of hyperthyroidism is confirmed with blood tests, and the Vet will also want to check for other common conditions that can affect older cats and cause similar symptoms. Hyperthyroidism can lead to other secondary problems, including heart disease, and it may be necessary to perform heart checks (including X-ray, ultrasound and ECG), at this stage, in addition to blood pressure measurement. How can the condition be treated? In the vast majority of cases (more than 95%), hyperthyroidism in cats is caused by a benign enlargement of the thyroid glands, and therefore treatment is usually very successful. The options are:
– Medical treatment: Anti-thyroid drugs are very effective at reducing the blood thyroid levels to normal in hyperthyroid cats. Cats that respond well to this treatment and do not have side effects will need life-long treatment, and also regular check-ups and blood tests to check that the dosage being administered continues to be effective. Once thyroid levels are controlled, most cats with high blood pressure and heart disease will see an improvement in these secondary conditions too, although some cats will need extra medication to help with these. The Vet will also want to monitor the kidney function of any cat on medication for hyperthyroidism, since renal failure is also another very common condition in older cats.
– Surgical treatment: Thyroidectomy (removal of the abnormal, hyperactive thyroid tissue) can be a very effective treatment option, particularly in those cats that have side effects on medication or respond poorly to anti-thyroid medications. It is usually only a good treatment option in cats that have obviously enlarged thyroid tissue that is accessible to surgery. Often surgery will cure the condition, but some cats will develop symptoms of hyperthyroidism again following successful surgery, if remaining normal thyroid tissue becomes hyperactive. Further treatment is then needed for these cats. There are some risks associated with surgery, including those risks associated with general anaesthesia, and also risk of damage to the parathyroid glands during surgery which can lead to low blood calcium levels. When such complications occur, they can usually be managed very effectively.
– Radio-active Iodine treatment: Iodine is used by the thyroid gland in the process of thyroid hormone production, and when radio-active Iodine is administered by injection to a cat with hyper-active thyroid tissue, it is taken up by the thyroid glands causing destruction of the abnormal tissue. This can be a very successful treatment option in most cats, with no serious side-effects. However, because it involves the use of a radio-active substance, cats treated this way usually need to be hospitalised for up to 6 weeks in a licensed hospital with handling kept to a minimum. A small number of cats may develop an under-active thyroid following radio-active iodine treatment, requiring thyroid hormone supplementation, but these cases are very rare.
Your cat has been diagnosed with hyperthyroidism- what is the right treatment option? Once a diagnosis of hyperthyroidism has been made, your Vet will discuss all treatment options with you, the pros and cons, and the relative suitability of each option for your cat. More than one treatment option may be used during the course of management of the condition in any individual cat, and continual monitoring is vital to ensure that the chosen option is managing the condition effectively. If you are concerned that your cat may have symptoms of hyperthyroidism, don’t hesitate to contact us here at the surgery to arrange an appointment for your cat to be checked. As with many conditions which affect older cats, early, accurate diagnosis is vital in maximising the chances of successful treatment and minimising the impact of secondary problems on the long term health of your beloved pet.