One of the more common feline diseases in senior cats is hyperthyroidism. Hyperthyroidism is defined as an overactive thyroid (ie. the thyroid produces too much thyroid hormone, thyroxin or T4). The thyroid is located near the trachea (windpipe) in the neck, and if it is enlarged it may be felt. The disease can occur as a result of a tumor (benign or malignant) on the thyroid gland or as a result of an enlarged gland. It is unclear as to what causes the thyroid gland itself to become enlarged. It is one of the most common feline endocrine disorders, as well as one of the most prevalent diseases in older (over 8 years of age) cats.

The thyroid controls metabolism in the body. So if your cat has hyperthyroidism his/her metabolism has sped up. This in and of itself is not only a problem, but it can also lead to other health problems such as heart murmurs, high blood pressure, cardiomyopathy (heart disease), kidney failure, arrhythmias and elevated heart rates.

Symptoms of hyperthyroidism are similar to that of some types of cancers, kidney disease and diabetes – all of which are serious problems. Thus if your cat has any of the below symptoms take her to the vet immediately for a proper diagnosis. A thyroid problem can be positively diagnosed by a simple blood test.

Symptoms to look for:

  • Excessive meowing or yowling
  • Increased thirst
  • Increase appetite
  • Increased urination
  • Increased defecation
  • Diarrhea
  • Vomiting more than once a week
  • Weight loss
  • Increased heart rate
  • Increased body temperature
  • Hyperactivity
  • Poor coat quality


There are currently three ways to treat hyperthyroidism:

  1. Radioactive iodine treatment. Treatment with radioiodine is an amazingly simple procedure requiring only an injection under the skin. The hyper functioning cells within the thyroid gland absorb and are destroyed by the radioactive substance. And, nearby normal cells are unaffected. The success rate is 90 to 95 percent after one treatment. This method is becoming more prevalent although it is still expensive ($750 to $1000) and is only performed in certain cities.
  2. Surgery to remove the abnormal thyroid tissue and affected lobe(s) of the thyroid gland. This can be a difficult procedure especially for older cats who are not as good candidates for anesthesia. The surgery option often appears initially to be successful, but the disease may recur later.
  3. Oral medication (Tapazole or methimazole) that blocks the production of thyroid hormone but does nothing for the cause of the problem. This drug must be given twice daily for the duration of the cat’s life. The biggest problem with oral medication is that many cats don’t do well with the side effects. This option may initially seem the cheapest solution. But over time medication costs add up and can actually end up being more expensive than the radioactive iodine treatment.

Hyperthyroidism is a controllable disease if caught early and treated appropriately. If you do not treat your cat he/she will die from complications of the disease or a compounded disease.

Precautionary measures:

As hyperthyroidism is thought to be inherited there are no real precautionary measures against this disease. The best precaution there is is early detection and treatment.