Hyperthyroidism In The Cat

They will hang around the owner’s legs in the kitchen and cry each time the fridge is opened …

Hyperthyroidism is a condition which most small animal vets will see quite frequently. Typically this will be an older cat say in the region of 13 or 14 years of age, at the initial consultation the owner will tell you that the cat appears to be thin and losing weight but paradoxically it is eating very well some cats may even show an abnormal interest in food and will hang around the owner’s legs in the kitchen and cry each time the fridge is opened. There are other signs you can look for as well, these would include a dull spikey coat, a pendulous abdomen and overactive behaviour, they may be thirsty and the faeces will be paler than normal and have a consistency like cow pats. In some cats the shape of the face changes and they are said to have a permanently worried look. This disease is the result of an overactive thyroid gland which in turn produces large levels of thyroid hormones, the disease is confirmed by running a blood test and measuring the levels of circulating thyroid hormone [ T4 ].

The thyroid gland is a bi-lobed structure located about half way down the neck close to the windpipe and when the lobes are enlarged they are quite easy to feel. Put very simply the thyroid gland’s main job is to produce thyroid hormone, hormones are chemicals that are secreted by glands which act like messengers telling specific body parts what to do. Thyroid hormones help the body make energy, keep body temperature regulated and assist other organs in their function. No one really knows the exact cause of this disease but it was first documented in the cat about thirty years ago.

As you can see from what I have written so far this disease is quite easy to diagnose both from clinical signs and a blood test but once we have our diagnosis how do we treat it. Well there are a number of options:

1. Radioactive Iodine. This is given by injection and has the effect of reducing the thyroid gland down in size, because iodine is not concentrated by any other cells in the body other than the thyroid gland there is very little radiation exposure (or side effects!) for the rest of the body, the radioactive iodine will build up in the thyroid and kill or disable the thyroid gland cells. The advantages of this treatment is that no anaesthetic is involved and the treatment is very simple. The down side is that it is expensive and the cat has to be kept in isolation for a number of days afterwards, also some cats can develop under active thyroid glands after this treatment.

2. Surgery. This is a relatively easy procedure which most small animal vets will be able to tackle, a portion of one or both thyroid glands is removed and logically this reduction in the gland will produce a reduction in circulating thyroid hormone. The advantage of this procedure is that you get an immediate beneficial effect and the cat usually requires no further treatment or medication. The down side of surgery is that of course an anaesthetic is required, care must be taken not to damage the parathyroid glands during surgery, some cats become hypothyroid [ reduced thyroid hormone ], and very occasionally the gland grows again and more surgery is necessary.

3. Medication. There are drugs available which will reduce the size of the thyroid such as Felimazole the active ingredient of which is thiamazole, provided there are no other complications these drugs can be very effective. The plus side to these drugs are that the owner can give them themselves in tablet form and initially this is the cheapest way forward. The down side to medication is that blood tests are needed a number of times a year to monitor the situation, some cats resent being dosed with tablets twice a day and can be difficult, this causes stress to both he cat and the owner, a small number of cats can develop side effects to the medication, these can include vomiting inappetance and lethargy. Owners should note that their cats may be on these drugs for the rest of their lives so the long term cost will mount.

So there we have it, a description of the disease, how it is diagnosed and how it is treated, but which treatment regime should you choose? Well of course your vet will talk you through this as all the forms of treatment I have listed can be effective. Iyou live close to a main referral centre such as a university centre and your pet is insured the radioactive iodine would be a good option, if your pet has other complications such as heart disease then you might want to avoid surgery and rely on medication. As I said your vet will talk you through all the options.

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This entry was posted on August 4, 2008 at 1:07 pm and is filed under Cat Diseases. You can follow any responses to this entry through the RSS 2.0 feed.