Feline hyperthyroidism is a very common disorder in older cats. It is caused by excessive production of thyroid hormone by the thyroid gland. It can lead to behavioral changes, hyperactivity, weight loss, high blood pressure, and heart disease.
One of the most effective treatments for feline hyperthyroidism is radioactive iodine (I-131). Once administered, the radioactive iodine concentrates within the thyroid gland and the emitted radiation destroys functional thyroid tissue without causing radiation damage to the normal parts of the thyroid gland or other tissues in the body. The advantage of this treatment is that it is both safe and effective.
In our program, the typical dose administered is 3-4 millicurie, with reduced doses considered for cats that have chronic kidney disease or very mild hyperthyroidism.
Side effects of the treatment may include a slight worsening of kidney function and some risk of reduced thyroid function (hypothyroidism). Before treatment we conduct several pre-diagnostic tests to help us determine the best dose needed for your cat. This keeps the risk of secondary complications very low.
Because radioactive iodine takes time to reduce to safe levels, cats need to be kept with us for a few days after treatment. The typical hospitalization period for evaluation and treatment in our facility is 5-7 days. Cats that share a home with children, pregnant women, or cats treated for malignant thyroid tumors may need to stay a few days longer.
Please bring enough of your cat’s usual food with them to last the duration of their stay (approximately 7 days), so that they can stay on the same diet they eat at home. You can also bring toys, blankets and a bed but these will not be able to be returned to you because of the risk of radioactive contamination.
We understand how important it is for you to feel prepared and informed. Knowing what to expect during your cats's visit can help the experience as smooth and stress-free as possible for both of you.
A Purdue Veterinary Hospital clinician and a veterinary student in small animal internal medicine will ask about your cat’s history, perform a physical examination, and review your cat’s test results. We will also collect a small blood sample to measure the pre-treatment total T4 concentration.
The lab work performed by your veterinarian is not likely to be repeated unless you report new concerns about your cat which have developed before your appointment with Purdue or if it has been over four weeks since the most recent lab work was performed.
If we identify any concerning abnormalities on our physical examination or prior lab work, additional tests we feel are necessary will be discussed with you.
If we determine that your cat is a good candidate for treatment, we will admit them to the hospital and order the correct dose of radioactive iodine for your cat. We will also make sure that they are comfortable and willing to eat in the hospital.
The following day we will administer the radioactive iodine treatment by injection under the skin (subcutaneous).
The radioactive iodine used in this treatment takes a few days for the radioactivity to reduce to safe levels.
During this waiting period your cat will have a private cage with a bed, litter box, and as much food and water as they want. Our staff will check on your cat at least twice a day.
Most cats only require a waiting period of 3-5 days. However, some cats may need to stay with us longer depending on circumstances.
When your cat’s radioactivity reading has dropped to a safe level, we will collect another small blood sample to measure the post-treatment T4 concentration. This allows us to make sure your cat has responded well to treatment.
Prior to taking your cat home, you will be asked to sign a release form which explains how to take care of your cat at home. We will provide instructions on how long your cat needs to be kept inside, how long you need to keep your cat at a safe distance after release, and how to dispose of the cat litter properly.
It is safe for cats to return to a home with other pets after treatment and even for them to share the same water bowls and litter boxes.
After release from the hospital, we recommend that the total T4, kidney function, and blood pressure are rechecked by your primary veterinarian at 1, 3, 6 and 12 months after treatment.
Here are some answers to questions we are frequently asked.
After being diagnosed with hyperthyroidism, your primary veterinarian should recommend trying a methimazole trial or food trial first, if applicable.
If you have discussed options and your veterinarian recommends radioactive iodine treatment, they will need to complete a referral form for the Purdue University Veterinary Hospital (SAIM) and submit documentation.
Once we receive your referral, someone from our team will call you to discuss treatment and schedule your pet’s appointment with us.
In order to accurately treat your pet for their disease, they must be off of any medication or diet that is actively affecting their thyroid levels. Radioactive iodine is a dose-dependent injection, so it is very important for us to know what your pet’s thyroid levels are without management to administer the correct dose.
These tests give us information that enables us to select the best dose of radioactive iodine for your cat. In our program, the typical dose administered is 3-4 millicurie, with reduced doses considered in cats that have chronic kidney disease or very mild hyperthyroidism.
The cost of this procedures varies depending on different factors including case. Please contact the Purdue University Small Animal Hospital to inquire about pricing.
The injection is given directly under the skin (subcutaneously) and only takes a few seconds. Most cats that are able to be handled do very well with being restrained for the short injection period. The injection shouldn’t hurt them other than a small sting for a short moment.
Most cats only need to stay with us for the minimum 72 hours after injection. After the 72-hour period, your cat is scanned to assess their radioactivity levels. Once the radioactive readings are at a safe level they will be released.
Pets that share a home with children, pregnant women, or immunocompromised individuals require an extended stay prior to being released. The extended period for pets receiving treatment is a minimum of 5 days after injection. After the 5-day period, your cat is scanned to assess their radioactivity levels. Once the radioactive readings are at a safe level they will be released.
Radioactive iodine takes a few days for the radioactivity to reduce to safe levels. Because the radioactive iodine releases through the patient’s urination and defecation, the time it takes depends on how often the pet is eating, drinking, and using the litter box in hospital.
No, your pet does not need to be isolated in a separate area once they return home. We recommend minimizing extended periods of contact with them, such as sleeping in the same bed.
Yes, but unfortunately, any items brought back into isolation during the waiting period will not be returned to you because of the risk of radioactive contamination.
You are more than welcome to bring special items to the hospital while your pet stays with us. This can make them feel more at home and more comfortable in a new setting. Many clients will bring things such as blankets, beds, t-shirts, treats, and toys.
Your cat carrier will remain outside of the isolation room, so your cat can return to you in the same carrier in which they were brought.
