Radioactive Iodine Therapy: A Scary Sounding Solution to a Common Feline Disease

by Lyn Garson

Fluffy is scheduled for the deluxe accommodations. Her reservation includes a private suite with a soft cozy bed and elevated lounging platforms. Warm sunlight pours in through the windows. Calming aromas and music fill the room. During her stay, Fluffy will enjoy breakfast and dinner while being entertained by the outdoor bird activity at feeding stations tucked among colorful flower gardens. When Fluffy enters the veterinary specialty hospital to begin her solitary retreat, she will be admitted for radioactive iodine therapy for a serious but common medical condition. When she leaves several days later, she will most likely be cured.

Radioactive iodine therapy, commonly referred to as I-131 radioiodine, is considered the treatment of choice for Feline Hyperthyroidism. Safe and effective, I-131 eliminates the disease without the typical side effects of daily medication or the risks associated with anesthesia and surgery.

More than 95% of cats are cured of hyperthyroidism with a single dose of radioiodine I-131. The injection is administered subcutaneously (under the skin) just like many routine vaccines. Anesthesia is not required for the procedure; however, a sedative may be given to ease any potential stress related to simply being at the veterinary hospital. Because the thyroid gland naturally uses iodine, the hyperactive thyroid cells absorb and are destroyed by the injected radioiodine without affecting normal thyroid tissue or any other structures in the body. In a majority of cases, this one-time injection is curative, however, a small percentage of cats may require a second dose. In rare instances, one to two percent of hyperthyroid cats may have a malignant thyroid tumor requiring different treatment protocols.

What is hyperthyroidism?
Feline hyperthyroidism is the most common endocrine disease, typically affecting cats over eight years of age. Seen in both sexes and all breeds, hyperthyroidism occurs when one or both lobes of the thyroid gland (located in the cat’s neck) become enlarged and produce an excess of thyroid hormones. This hormone increase overstimulates the heart, kidneys and digestive system, forcing them to work much harder than under normal circumstances. In most cases, thyroid enlargement is caused by a benign (non-cancerous) tumor called an adenoma. Cancerous thyroid tumors are rare and found in only two percent of cases.

Signs and Symptoms
The classic signs of hyperthyroidism – weight loss despite an increased appetite, and excessive thirst along with frequent urination – may be very subtle in the early stages, making them difficult to detect. Myriad other symptoms can also appear such as behavioral changes, hyperactivity, vomiting, diarrhea, muscle wasting, and a greasy or matted coat condition. If left untreated, hyperthyroidism causes damage to multiple organ systems which can potentially become life threatening.

To reach a diagnosis, your veterinarian will perform a physical examination which includes palpation of the thyroid gland in the front of the neck area to check for enlargement. Heart rate, respiratory rate and blood pressure are measured, and muscle mass is assessed. Blood tests are conducted specifically for thyroid function levels as well as general screening for secondary issues or other potential health conditions.

Radioiodine Therapy Hospitalization
Radiation safety regulations require I-131-treated cats to remain in a specially designed suite within the hospital, typically for three or four days, but in some cases, seven to ten days. During this post-injection treatment period, cats excrete the radioactive iodine so direct contact with them is not permissible, however, some facilities have webcams to provide pet parents the opportunity for live virtual visits around the clock.

Post-Treatment Home Safety Precautions
Upon discharge from the hospital, cats treated with radioiodine emit radiation levels comparable to the level humans experience when being outside in the sunshine. However, for everyone’s safety it is imperative to follow all precautionary guidelines at home for the first two weeks or longer, depending on which state you reside in, as each state has different regulations. This will include confining your cat indoors, avoiding prolonged physical contact with your cat, and not allowing them in the bed with you. In addition, because the radioiodine is eliminated via the urine (just like in people treated with radioiodine) specific procedures will be explained to safely dispose of litter box contents. Other cats in the household do not need to be separated and may interact with your cat post-treatment, as well as safely share food, water and litterboxes. Dogs in the household should not be allowed contact with the litter box as this could be damaging to the dog’s normal thyroid function.

Advantages of Radioiodine Treatment
Most cats’ thyroid function returns to normal within several weeks of being treated with radioiodine, eliminating the dependency on daily medications. Although the cost of this type of therapy is greater up front, if you consider that ongoing daily medications are no longer needed, it is more economical in the long run. Also, I-131 is safer than surgery which requires general anesthesia. Best of all, cats of any age can be cured with a single injection.

Radioiodine may sound scary, but it’s a solution with glowing results – the renewed vigor of good health and a much brighter quality of life.