Feline hyperthyroidism is the most common endocrine disease in cats, affecting about 10% of cats that are over ten years old. This disease is caused by an overactive thyroid gland (or glands; cats have two) due to a non-cancerous tumor, which results in more thyroid hormone being made than the cat’s body needs. High levels of thyroid hormone can result in weight loss, changes in appetite, increased thirst and urination, hyperactivity, vomiting, and diarrhea. Over time, heart disease can also develop.

I-131 treatment, or radioiodine therapy, is a very effective way to treat hyperthyroidism in cats. It has very few side effects, and once completed, the cat does not need ongoing treatment. Other treatments for hyperthyroidism tend to have more side effects, or require long-term medication, so I-131 treatment is often preferred. In I-131 treatment, a radioactive isotope of iodine is injected under the skin (like a vaccine) and the tumor absorbs it. The local radiation kills the abnormal cells with very few side effects. Once the cat’s thyroid levels return to normal, they are considered cured and do not need ongoing treatment.

The Animal Emergency and Referral Center of Minnesota (AERC) performs I-131 treatments, and is where Mellie will be going for hers. They have a very nice facility, possibly the best in the country, for cats that are undergoing I-131 treatment. Each cat has its own large kennel, with windows, multiple levels, and separate areas for a litterbox, sleeping, and eating.

Cats that are having I-131 treatment arrive at the AERC on Monday morning for their initial consult, which will screen for any concerns that would prevent them from being able to have the treatment. A treatment plan is created specifically for each individual cat. The cats then stay in the hospital overnight and get their radioiodine injection on Tuesday. No anesthesia or surgery is needed. They can go home after their radiation levels are below the state mandated level, which is on Friday for about 80% of patients. The rest go home on Saturday. Owners can visit their cat at the AERC, viewing them through a nursery-style viewing window, or they can log in and monitor their kitty via webcams that are available around-the-clock.

After returning home, a few precautions are necessary for the first three weeks to minimize radiation exposure for the cats and people who live with the patient. Complete isolation from people is not required, but exposure should be very limited. Among other things, treated cats must be kept separate from other cats and use separate food and water dishes, and litter boxes, because radioiodine in excreted in the urine and saliva. Because of this, you won’t see Mellie roaming around the hospital for the three weeks following her I-131 treatment.

For more information, please visit the following: