The thyroid gland sits near the trachea (wind pipe) and regulates metabolism. In many cats (median age is over 10 years) the gland begins to grow and/or over secrete hormone. This can result in high blood pressure, enlarged heart, vomiting, diarrhea, the need to eat and/or drink more, weight loss, blindness and in some cats we notice a change in their temperament to more cranky.

There are no specific known breeds or environmental situations that make a cat more or less likely to become hyperthyroid.

To diagnose this disease, a through physical exam is conducted including a proper history, weight, blood pressure, a retinal exam. From there it will be determined what laboratory tests or x-rays should be done. Most commonly done first are blood tests looking for thyroid horomone in two states (T4 an Free T4), basic liver and kidney functions and a urinalysis.

Once it is diagnosed, there are two main ways to treat this condition.

1. Medicine: There are pills, liquid or topical forms of methimazole that can be given to the cat to reduce thyroid hormone production. This is done in almost every case – sometimes for the life time of the cat – sometimes before looking at a more permanent fix. The medicine has to be given twice a day, is usually fairly affordable, and requires periodic recheck labwork be done to monitor the effects of the medicine. In the end this is a good therapy option for very old cats, or for cats who have other underlying diseases – like renal failure.
2. Radioactive iodine therapy: Once a cat has had a methimazole trial (not always required but usually done) some owners elect to have a more permanent fix. This method requires going to a specialist where a radioactive isotope of iodine is given intravenously to the cat. The iodine is selectively taken up by the thyroid gland only and destroys a carefully calibrated amount of thyroid tissue permanently. After a few follow up tests most cats remain in a normal thyroid (euthyroid) state for the rest of their lives. This can be a great option for younger, healthier cats who have done well with a methimazole trial. In the long run this is a more cost effective method of treatment in some cases.

The prognosis is usually very good for hyperthyroid cats who receive regular and appropriate treatment and monitoring. Left untreated, cats can develop fatal heart conditions, blood clots, or malnutrition leading to death. Most importantly they do not lead a good quality of life and may suffer for lack of treatment.

While there is no specific way to prevent this disease, appropriate monitoring – starting around age 7 – can help catch the disease early and lead to the best possible outcome if diagnosed.

For further information please contact your veterinarian.