This is one of the most commonly diagnosed hormone diseases in cats.
We see many cats suffer from an overactive thyroid. Many of you might put the signs just down to ageing. Over the last 20-30 years a great deal of research has been done on this disease, and treatment has improved as a result.
The thyroid glands sit in the neck, one either side of the windpipe, with occasional extra smaller glands present elsewhere in the body in some cats. The glands produce thyroid hormones which are involved in regulating metabolism, so they have an effect on most systems of the body, ie. the heart, liver, kidneys, blood pressure etc. The glands can become enlarged and overactive, producing too much thyroid hormone. This is usually because of a benign (non-cancerous) change in the thyroid gland, but more rarely it can be caused by a nasty tumour called a thyroid carcinoma.
The typical cat with hyperthyroidism will be a middle aged to older cat with some or all of the following symptoms:
- always loss of weight
- always increased appetite (constantly asking for food)
- occasionally increased thirst
- increased heart rate
- heart murmur
- restlessness or hyperactivity
- digestive upset (vomiting and diarrhoea)
- an unkempt coat
- swelling of the thyroid glands in the neck
These sorts of symptoms will make us suspicious that hyperthyroidism is the cause, but it can only be confirmed with a blood test to measure the levels of thyroid hormones. We usually combine this with other tests to check kidney and liver function and to check for diabetes, as all these can have similar symptoms and of course there might sometimes be more than one problem going on.
If hyperthyroidism is diagnosed, we usually begin treatment with tablets that reduce the production of thyroid hormone. The tablets cannot be crushed or split! The dose and frequency will depend on which drug is used and on how high the thyroid hormone levels were on the blood test. After 2 or 3 weeks a second blood test will show us whether the levels are becoming closer to normal, at which time the dosage may be changed. If this treatment suits your cat, it can be continued long term with regular monitoring by blood tests.
However, some cats are harder to give tablets to than others, and a few will suffer from side effects. We now have this medication available as a gel that you can smear into the cat’s ear twice daily if tablets are too difficult to give to your cat. This product is still very new, so our experience is a bit limited.
Another treatment option is surgical removal of the thyroid glands. The operation does involve some risks, particularly the risk of damaging other small structures next to the thyroids, like the parathyroid glands. (These are important in regulating the levels of calcium in the blood, and if damaged during surgery supplementation with calcium could be needed.) A cat with heart problems may be a poor risk for surgery, but often tablets can be used first to improve health so surgery is a better option, and additional drugs to control any heart problems may be given. In most cases, cats which have had their thyroids removed will not need to take tablets, but often the problem can still return later, if for example the cat has some smaller gland tissue which was not removed with the main glands. This extra thyroid tissue can be located anywhere in the neck or even within the chest.
In some cats only one thyroid is affected at first so only one is removed, then some years later the same condition could occur on the other side. We rarely perform this operation - it is a bit out of fashion now. The other main treatment available is with radioactive iodine, which is a specialist treatment only available at some centres in the UK. Chris has been treating many cats with this treatment when working at the Barton Veterinary Hospital in Canterbury. Radioactive iodine is given to the cat by injection and it becomes concentrated in the thyroid gland, where the radioactivity destroys the damaged tissue. One of the disadvantages of this treatment is that the cat has to be hospitalised for several weeks because of safety issues surrounding the radioactive material used. It is not dangerous to the cat itself but has to be handled safely to protect people working with it. The cost of this treatment is around £1500!
Hills Petfood has recently developed a new diet Y/D. This is a diet that does not contain any iodine. Iodine is needed by the thyroid gland to produce thyroid hormone. No iodine - no hormone (in theory at least). We had some decent success with this diet but it is essential your cat only eats this diet - no milk, no feeding at neighbours, no catching mice!
We still need to see how successful this treatment is long term... Decisions on which treatment would be best for an individual cat are best made in conjunction with us at White Cliffs Vets. Where complicating factors like heart disease or kidney disease are present, these need to be treated as well. Once diagnosed, the outlook for a cat with hyperthyroidism is usually very good.
Whichever treatment is used, it is likely to prolong life and improve the quality of life.