Feline Hyperthyroidism and Radioactive Iodine Therapy (I-131)

Hyperthyroidism is the most common endocrine disorder in middle aged and geriatric cats. Symptoms of hyperthyroidism can include behavioral changes, hyperactivity, weight loss, increased appetite, increased thirst and urination, vomiting, diarrhea, and rapid heart rate. Your veterinarian may diagnose hyperthyroidism through physical examination findings and/or routine laboratory findings. Once a diagnosis of hyperthyroidism is made, your veterinarian will discuss options for treatment, which include medical management, surgery or radioactive iodine (I-131).

If radiation therapy is elected, Animal Imaging can provide I-131 treatment in a safe and comfortable environment for your cat. Radioactive iodine is an effective and safe treatment for hyperthyroidism. Cats treated with radioactive iodine receive a subcutaneous (under the skin) injection of the drug and are then hospitalized until the level of radiation is low enough for your cat to safely return home. Once your cat returns home, precautions that you and your family will need to take to ensure your safety at home are as follows:

  • Children under the age of 18 and pregnant women should have no contact with the cat or soiled kitty litter for 14 days after arriving home. All others should limit contact to petting and holding for brief periods. Kissing and contact with the face should be avoided for the first 14 days. Hands should be washed after contact, and especially before any food handling. If it is necessary for your pet to be medicated, disposable gloves should be worn.
  • Do not allow your cat to sleep in the bed with family members for the initial two week period. This may require that your cat be isolated to a specific room of the house. The cat should not be allowed on any food preparation surfaces.
  • A separate litter box should be used for the treated cat. A plastic liner should be placed in the box, then commercial cat litter poured over the liner. The person cleaning the litter box should wear protective gloves made of rubber or plastic. The litter may be scooped into a plastic bag, which is then sealed and discarded in the regular trash. The litter box should not be in an occupied bedroom or in the kitchen. It should also not be kept where children may come in contact with the litter.
  • If your cat vomits or soils outside the litter box, wear disposable gloves when cleaning up. Routine household cleaners may be used. Dispose of all soiled cleaning materials in a plastic bag in the regular trash.
  • Your cat should be isolated to your house and should not be allowed to roam outside for the initial two week period. This is to prevent contact with others unaware of the radiation.
  • At the end of the two week period, discard any remaining litter and any gloves used to change the litter. At this time, any residual activity in your cat is considered gone and you may return to your normal routine.

A few screening tests will need to be performed prior to your cat undergoing I-131 therapy. Those tests include:

  • A chemistry profile (blood work) to screen for other underlying illnesses such as kidney disease. This test is performed by your referring veterinarian.
  • A urinalysis to screen for kidney disease. This test is performed by your referring veterinarian.
  • A thyroid scan to evaluate the thyroid itself and check for benign or malignant thyroid disease. The thyroid scan can be performed at Animal Imaging on an outpatient basis.

Once the screening tests are performed and your cat is determined to be a good candidate for I-131 therapy, arrangements can be made at Animal Imaging to administer the therapy. Most cats are admitted to Animal Imaging on a Monday and can return home on a Friday.

Frequently Asked Questions:

Q: Can I bring any toys, bedding, food, etc. for my cat?
A: We recommend that you bring your cat’s regular diet so that we can maintain him/her on what you normally feed at home, although we can provide food if necessary. Toys and bedding are permitted, but due to the radiation levels in the I-131 therapy area, those items will be discarded at the end of your cat’s stay.

Q: Can I visit my cat during his stay?
A: Unfortunately, we cannot allow visits during your cat’s stay due to the radiation levels. We do, however, encourage you to call and check on your cat’s status as often as you like.

Q: Will my cat experience any side effects from the drug?
A: Very rarely (approximately 2% of treated cats) cats may become hypothyroid after administration of I-131. In such cases, these cats can return to normal with supplementation of thyroid medication. Some cats may experience a few weeks of lethargy after returning home. These side effects are rare and the benefits of treatment far outweigh the risks of no treatment at all.

Q: What follow-up care do I need to provide for my cat
after therapy?
A: Your cat’s thyroid levels should be recheck approximately 2 months after treatment to ensure that the thyroid has returned to normal. This test can be performed at your regular
veterinarian’s office.