Radioactive Iodine Therapy for Feline Hyperthyroidism

Hyperthyroidism is the most common hormone disorder in cats. It is caused by growths within the thyroid gland which lead to excess thyroid hormone in the body. Thyroid growths are usually benign but can be malignant in rare cases.

Common symptoms of hyperthyroidism include hyperactivity, weight loss and increased hunger. Some cats will become more vocal and thirsty, and many hyperthyroid cats also urinate more than usual. Occasionally, cats will not show any symptoms of hyperthyroidism but the disorder can be detected during wellness testing by your veterinarian.

Fortunately for your cat, this is a very treatable problem with several management options:

1) Methimazole (generic, Tapazole TM, FelimazoleTM) is a medicine which inhibits the production of thyroid hormone, thereby resolving symptoms of hyperthyroidism. This treatment is highly effective, readily available, and not very costly in the short term. The medication can be administered orally as a pill or liquid, or topically on the skin. This treatment must be monitored periodically to make sure it is working properly and not causing side effects. It is important to note that this treatment does not cure hyperthyroidism, but usually can control the problem as long as the medicine is given regularly as prescribed by your veterinarian.

2) Nutritional Therapy involves feeding a special diet, restricted in iodine content, which can help lower thyroid hormone levels.  

3) Surgery can be performed to remove the abnormal thyroid tissue. This treatment has been effective in curing hyperthyroidism in many cats but is less popular recently as safer and simpler options are now readily available.

4) I-131 (radio-iodine) therapy is a form of nuclear medicine used to cure feline hyperthyroidism. This is a very simple, safe and highly effective treatment. The vast majority of cats treated with I-131 will be cured of hyperthyroidism. The American Association of Feline Practitioners considers I-131 to be the treatment of choice for hyperthyroid cats.  

How does I-131 work?

The thyroid gland is the only part of the body that uses iodine, a nutrient that is essential to synthesize thyroid hormones. I-131 is a form of iodine that is radioactive. I-131 is given by injection and circulates in the blood until it is taken into the thyroid gland. In hyperthyroid cats, the cells within the abnormal nodules are actively making an abundance of thyroid hormone, but the normal thyroid tissue is suppressed and not making any thyroid hormone. Therefore, only the cells within the nodules will absorb the radioactive iodine. Once inside the abnormal thyroid cells, the radiation goes to work to destroy the abnormal cells. Small amounts of radiation will be emitted from your cat during the treatment, so strict isolation in our facility is required to keep everyone safe. Once the level of radioactivity is below a certain limit, usually within a few days, the cats are safe to go home.

Why choose VCA VRA to perform I-131 on your hyperthyroid cat?

We are the only facility in Maryland to offer I-131 with 24-hour on-site doctor supervision of your hyperthyroid cat.

We are also the only facility in Maryland to offer board certified specialists to oversee your hyperthyroid cat’s care before, during and after the I-131 treatment.

We are the only facility in the mid-Atlantic area to offer a thyroid scan before I-131, which is useful to confirm the diagnosis of hyperthyroidism, confirm the location of the abnormal thyroid glands, and suggest if hyperthyroidism is due to a benign or malignant tumor. The results of the thyroid scan also help determine the dose of I-131 needed to treat your cat’s hyperthyroidism.

What is included in the I-131 therapy of my hyperthyroid cat at VCA VRA?

A consultation with a board certified internal medicine specialist is an important first step in the treatment of your hyperthyroid cat at VCA VRA. An internist will examine your cat and carefully review the medical history including all prior tests and treatments, especially those related to the diagnosis and treatment of hyperthyroidism. An internal medicine consult is important because hyperthyroidism tends to be a disorder of older cats that may have other age-related problems occurring at the same time. Your cat’s blood pressure will be evaluated as well; many hyperthyroid cats have high blood pressure due to hyperthyroidism or other problems.

I-131 is administered by specially trained personnel via injection (one shot) and then your cat is allowed to rest for several days until the levels of radioactivity are safe for him/her to rejoin your family. During the time your cat is here, we will visit him/her twice daily to provide fresh food, water and bedding, clean their litter box, check their levels of radiation, and also to provide some well-deserved tender loving care. While we cannot be with your cat for a long period of time because of radiation safety guidelines, we do have someone watching your cat to make sure they are safe and sound at all times through video monitoring. Cats are admitted on Monday mornings and discharged on Fridays. We will communicate the results of all of our exams, recommendations and treatment for your cat with your regular veterinarian.

What do I need to do once my cat is home from I-131?

Your cat can resume its normal routine at home with a few restrictions. For 17 days after your cat goes home from I-131, he/she should remain indoors and not sleep or sit near your head or on your lap. These recommendations are to protect you from the tiny amounts of radiation that are still being emitted from your cat during this time. Your cat can eat its normal diet and use the litter box as usual. Special recommendations on handling your cat’s waste during this time will be provided to you.

1, 3, and 6 months after I-131, it is recommended that you bring your cat back to VCA VRA or to your veterinarian for post I-131 monitoring. The monitoring is helpful to make sure the I-131 treatment was effective in curing your cat’s hyperthyroidism, to evaluate if the thyroid levels are adequate, and that the rest of your cat’s body systems are functioning smoothly too.

For questions or further information about I-131 therapy, please call Veterinary Referral Associates and one of our staff members will be happy to speak with you about it.

Internal Medicine

A board certified veterinary internal medicine specialist is a licensed veterinarian who has obtained intensive, additional training in... More

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