Radioactive Iodine Therapy (I-131)
The Treatment of Choice for Feline Hyperthyroidism
Hyperthyroidism is a clinical condition resulting from the excessive production of thyroid hormones by the thyroid gland, and is common in middle-age to older cats. In fact, more than 95% of cases occur in cats over 8 years of age. This is usually due to benign changes (hyperplasia or adenomas) in the thyroid gland. Cancer of the thyroid gland can occur in cats, however it is rare.
Symptoms of an Overactive Thyroid
- Weight Loss
- Increased Appetite
- Polydipsia – Increased Thirst
- Polyuria – Increased urination
- Hyperactivity or lethargy
- Behavioral changes
- Cardiac Issues:
- Tachycardia – rapid heartbeat
- Heart Murmurs
- Arrhythmias – irregular heartbeat
John Lucy, DVM, DACVIM
Reena Shah, DVM
To schedule an appointment or consultation please call us at 201.262.0010
Treatment Options For Feline Hyperthyroidism:
- Anti-thyroid medications – Methimazole (Tapazole), Ipodate
- Surgical removal of the thyroid gland
- Radioactive Iodine (1-131)
Medical treatment consists of giving oral medication two or three times daily for the remainder of the cat’s life. The medication does not cure the disease; it merely controls the release of thyroid hormone. There is an incidence of side effects such as vomiting, diarrhea, poor appetite, and skin lesions. Missed medication will result in relapses. Surgical removal of the affected thyroid gland(s) will cure the disease, however, there are risks of anesthesia and surgical complications in older and often frail cats.
Radioactive Iodine Therapy
Radioactive Iodine (I-131) is a safe and effective, minimally invasive option to treat cats with overactive thyroids. Following one subcutaneous injection of I-131, over 98% of affected cats are cured of the disease. If needed, a second injection can be given. There are no harmful side effects.
Cats remain in the hospital for approximately four days until the radioactivity is below the legal level as determined by the nuclear Regulatory Commission (NRC). For the comfort of your cat, and your own peace of mind, we have a designated I-131 treatment room that your cat will remain in during their short stay.
How Does Radioactive Iodine Work?
Iodine is normally taken up by the thyroid gland. One form of iodine, I-131, is radioactive. When I-131 enters the thyroid gland it destroys the abnormally functioning cells. This reduces the size of the gland and its ability to produce thyroid hormone. I-131 is administered to hyperthyroid cats by a subcutaneous injection. Cats treated with radioactive iodine need to be hospitalized for 4-7 days following the injection. This is when they are most radioactive. Their level of radioactivity is checked daily with a Geiger counter and only when it reaches an acceptably low level as determined by the Nuclear Regulatory Commission (NRC) can they go home.
John Lucy, DVM, Diplomate, ACVIM (Internal Medicine)