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Feline Hyperthyroidism

Tampa Bay Animal Hospitals | Tampa, FL
By Dr. Susan Vaughn

Feline hyperthyroidism is caused by overproduction of thyroid hormones that is most commonly due to either a benign tumor or hyperplasia (excess tissue growth), though there is a risk of it being due to a malignant thyroid tumor. An increase in thyroid hormones results in an increase of the metabolic processes in the body, thus resulting in clinical signs such as weight loss in spite of an increased appetite. Hyperthyroidism can also affect the heart, blood pressure, kidneys, a pet’s behavior, hair coat, and others.

There are several treatment options for hyperthyroidism including radiation therapy with radioactive iodine (I-131), medical treatment with oral medications, prescription diet, and surgical removal of the thyroid gland. Treatment with radioactive iodine is the current gold standard treatment where the radioactive iodine concentrates and destroys some of the thyroid tissue. This treatment is done in hospitals that have undergone special
licensing and patient’s are typically kept hospitalized at the facility for a period of 3 to 10 days. Medical treatment is achieved by administering a medication called Methimazole that ultimately affects the formation of the thyroid hormones but does not affect the thyroid gland itself. It must be given one to two times per day as decided by your veterinarian based on follow up bloodwork.

Hill’s Science Diet has a prescription diet called Y/D that has limited levels of iodine in it, which is needed to form thyroid hormones. The key with feeding the prescription diet is that it must strictly be fed alone because many other foods, treats, and nutraceuticals contain iodine in them that would offset the therapeutic effect of the diet. Another option for the treatment of hyperthyroidism is removal of the thyroid gland. The surgery is not without risks though, as an important and smaller gland (the parathyroid gland) sits along each side/lobe of the gland, and there is a risk for accidental removal or injury of this gland that can result in complications. Additionally, surgical removal of the thyroid gland is recommended to be done as a two step surgery– where one side/lobe of the gland is removed initially, and then the other side/lobe is removed several weeks later.

Finally, follow up testing is crucial to treating hyperthyroidism. Because the excess thyroid hormone and subsequently increased metabolism effects so many other body organ systems, it is common to “unmask” previously hidden chronic kidney disease. Proper treatment of hyperthyroidism and regular recheck exams and diagnostics can help extend a pet’s life and quality of life.

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