Feline Hyperthyroidism, the causes, symptoms and treatments.
A cat's thyroid glands produce the hormones used to control the animals metabolism. The glands are situated on the underside of the cat's neck along its trachea (windpipe.)
If the thyroid glands become overactive they release an excessive level of hormones into the bloodstream.
This can have a damaging effect on the cat's health including, high blood pressure, uncontrolled weight loss, heart disease, kidney disease and liver damage.
Over-activity can be caused by enlargement of the thyroid glands or by a non cancerous tumor. It is rare that this condition is caused by cancer.
In about eighty percent of cases both thyroid glands are affected.
This is very much a disease that effects cats over the age of ten years, it is rarely found in a younger cat.
There is very little evidence that certain breeds are more prone to feline hyperthyroidism, all older cats can be effected, both male and female.
There are three basic options for treating this feline disease available today. One of the options does not in any way cure hyperthyroidism but helps to control it.
All three options have advantages and disadvantages.
Administering antithyroid drugs such as methimazole is perhaps the most widely available method of treatment.
It is often the only suitable method of treatment for cats who also have kidney disease.
Antithyroid drugs control the output of thyroid hormones and many cats progress well with drug treatment.
However this method of treatment is not a cure, the drugs have to be administered every day, usually twice daily, for the rest of the cat's lifespan.
Periodic checks are needed to test the cat's hormone level and if necessary the veterinarian can adjust the dosage.
Should the antithyroid drug treatment be stopped then the symptoms of feline hyperthyroidism will quickly return.
Because there is the possibility of side effects, the veterinarian will likely prescribe a low dosage at the start of the treatment, increasing by small amounts if all is well, until the most effective dosage is reached.
Some side effects will subside as treatment continues, but with others the treatment will need to cease.
Although the initial cost of antithyroid drug treatment may seem low (compared to surgery and radioactive iodine treatment,) the cost of the drugs can mount up depending on the life expectancy of the cat. There will be other expenses as well, such as the periodic testing.
The disadvantages may be:
Surgical treatment is an option and can be very effective, however it is not suitable for all cats suffering with feline hyperthyroidism.
The operation requires the skills of a veterinary surgeon experienced in thyroidectomy.
The cat will stabilized with methimazole for a short period before the surgery and a scan will be taken to establish how much diseased tissue there is.
The operation must be performed with great care as the cat's thyroid glands are clustered with other sensitive glands and nerves.
Often the surgeon will use caution in regard to the amount of tissue that is removed, the animal is then monitored and, if necessary, more tissue is removed in a second operation.
The points in favor of surgical thyroidectomy :
The points against surgery.
Radioactive Iodine Treatment ( I-131)
This treatment is performed at a specialist veterinary unit.
The hyperthyroid cat is given an injection of radioactive iodine, in the vast majority of cases one injection is enough for the treatment to be successful.
The iodine travels through the cat's body to accumulate in the thyroid glands where it destroys the over-productive cells while leaving the normal cells alone.
The cat will then need to be hospitalized, in isolation, until radiation levels decrease. The length of isolation depends on state laws, but is usually one to three weeks.
That is usually all there is to radioactive iodine treatment. In a very small number of cases the procedure will need to be repeated and approximately one in twenty cats will require daily thyroid hormone supplements.
The big pluses of this method of treating feline hyperthyroidism are:
Some disadvantages to radioactive iodine therapy:
Unfortunately there does not appear to be any statistical information on the expected lifespan of cats that have had feline hyperthyroidism treatment, at least none that is publicly available.
This may be because most cats with hyperthyroidism will likely be of advanced years anyway, plus the varied methods of treatment and how advanced the disease was before treatment commenced.
Also any other diseases or illnesses the cat is suffering from would need to be taken into account.
A hyperthyroid cat left untreated does not have a good outlook, most will likely become increasingly scrawny and weak, severe health problems are very probable such as heart disease and strokes.
If your cat is diagnosed as having hyperthyroidism, the veterinarian will want to discuss with you the best course of action.
The vet will take into account, the age and condition of your cat, the presence of any other diseases, the availability and suitability of various treatments and your views and opinions.
Sometimes a cat may be found to be hyperthyroid, perhaps during a routine examination, but is not yet showing any of the symptoms. In these cases, a wait and see approach may be adopted with the cat being regularly monitored to see how the disease progresses, before a firm decision about treatment is made.
This page was not written by a veterinarian. It is intended to provide information about feline hyperthyroidism and not as a substitute for professional advice.
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