Feline Hyperthyroidism

Hyperthyroidism, or overactive thyroid gland, is a relatively common disease in older cats.  The thyroid gland is located in the front of the neck, and is responsible for secreting a hormone, T3, throughout the body.  This hormone is converted to its active form, T4, in the cells of the body.  The amount of T3 and T4 in the body acts as a sort of metabolic “thermostat” and sets the metabolic rate.  When the thyroid hormones are elevated a cat’s metabolic rate is elevated as well, and this can cause worrisome symptoms.

Elevated thyroid hormone in cats is most commonly due to a benign growth within the thyroid gland, called a goiter.  This is not a true cancer – less than 5% of all hyperthyroid cats have thyroid cancer.  Some symptoms that you may notice in your cat if hyperthyroidism is present are:

  • Weight loss despite a good (or even increased) appetite
  • Increased thirst and urination
  • Urinating outside the litterbox
  • Chronic intermittent vomiting or diarrhea
  • Restlessness and agitation

Hyperthyroidism is diagnosed by a blood test to check for the level of T4 in the bloodstream.  Most often we will also check for other common causes of disease in older cats, like chronic kidney disease or diabetes mellitus to make sure that the elevated thyroid hormone is really the cause of the issue.  Hyperthyroidism can cause more serious silent diseases, such as heart disease and high blood pressure.  Since this is the case treatment should always be pursued for cats with hyperthyroidism.    

Cats with hyperthyroidism can go on to live relatively normal lives.  Treatment for hyperthyroidism can vary depending on each individual cat’s needs.  Possible treatment options include daily medication, dietary changes, surgical removal of the thyroid gland, or radioactive iodine used to inactivate the thyroid gland.  If your cat is diagnosed with hyperthyroidism we will go over the treatment options and make the best plan for you and your pet.

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