About the Thyroid Gland

About Feline Hyperthyroidism

The thyroid gland is composed of two lobes, one located on each side of the trachea just below the larynx. The thyroid gland produces a hormone called thyroxine (T4) and is responsible for maintaining the body's normal metabolic rate, which affects the function of many body organs.

Feline hyperthyroidism is a disease that commonly occurs in middle aged to geriatric cats. Hyperthyroidism is the result of the thyroid gland overproducing thyroxine (T4). The excessive T4 causes the metabolic rate to increase. The thyroid gland may become enlarged. Cats that have hyperthyroidism typically show symptoms of increased appetite while losing weight, excessive thirst and urination, and sometimes hair loss. Cats with hyperthyroidism frequently experience a reduced quality of life due to weight loss, muscle deterioration, chronic vomiting or diarrhea. In addition, some hyperthyroid cats present less visible signs of the disease such as heart disease and high blood pressure. Left untreated, these problems can be life threatening. However, these conditions can be prevented with timely treatment for thyroid disease.


How Feline Hyperthyroidism is Diagnosed

Feline hyperthyroidism can be suspected by your veterinarian based on clinical signs (symptoms) and physical examination. The diagnosis must be confirmed by taking a blood sample to test for elevated thyroid hormone (T4). Hyperthyroidism also may be detected from result of blood tests done at the time of annual physical examination allowing early diagnosis and treatment.

I-131 Radiotherapy is the Safest and Most Effective Treatment Option

Radiotherapy is the safest and most effective method of treatment for feline hyperthyroidism. In this non-invasive treatment, a small amount of radioactive iodine (I-131) is injected under the cat’s skin and is taken up by thyroid tissue without endangering other organs. Radioiodine kills the thyroid cells to return the gland to normal function. While most cats return to normal levels of thyroid hormone production within 2-3 months, a small number can take up to six months or more to return to normal function. By law, the treated cats must be held in hospital for at least 3 days after treatment. This ensures radiation levels are safe for the cat to be returned home with their owners. 

Treatment Requirements

After Treatment Requirements

Cats should have complete lab work including CBC, blood chemistry panel with T4, and urinalysis obtained by their primary care veterinarian prior to referral for treatment. Additionally, no anti-thyroid medications can be given for at least 7 days (preferably 10-14 days) before treatment because these medications can block effective treatment with radioiodine. The cat should be in a non-compromised condition and deemed treatable by the referring veterinarian.

Your cat will need to be quarantined at home for 2-3 weeks after treatment and we will carefully discuss the aftercare. You and your cat should revisit your primary care veterinarian for follow up lab work including appropriate blood chemistry with T4 and urinalysis approximately 2-3 months after treatment.