Radioiodine is the gold-standard treatment for feline hyperthyroidism, almost always curing the condition.

Radioiodine is the radioactive isotope Iodine-131. It destroys thyroid tumors, thereby curing hyperthyroidism. There are many advantages to radioiodine treatment – for example, it is non-invasive, painless, permanent, and has no side-effects.

In most cats, hyperthyroidism is caused when a portion of the thyroid gland becomes overly active, loses its normal regulation, and secretes excessive amounts of thyroid hormone. However, in a small percentage of cats, hyperthyroidism is caused by thyroid cancer. It is important to determine which problem is present in your cat since the treatment and expectations for the future of your cat depend on the cause of hyperthyroidism. We attempt to answer this question during the evaluation of your cat before treatment.

Radioiodine is now very well established as a treatment for thyroid tumors in humans as well as animals, so you needn’t worry that it’s experimental or unproven. This type of treatment is very specialized, however; we have to be licensed to handle radioactive materials, and as one of Texas’ largest radioiodine treatment centers, we are very experienced in advising pet owners on safety once their cat has returned home.

The isotope is given as an injection under the skin at the back of the neck.

Radioiodine is absorbed very quickly into the bloodstream and then gets taken up by thyroid tumor tissue – and no other kind of tissue, including healthy thyroid tissue. It becomes concentrated in the tumor, and the beta-radiation it emits kills the tumor. Since any thyroid tumor acts as a ‘magnet’ for radioiodine, the treatment will also tackle any tumors in the chest (which are notoriously more difficult to identify and treat) as well as the more common tumors in the throat. Because cats undergoing this treatment emit radiation while the radioiodine is in their body, they must be temporarily isolated from people and other animals during the treatment period.

Radioiodine is an appropriate treatment for cats

with hyperthyroidism that are in a stable medical condition. Because these cats are emitting radiation during this treatment, only basic care (feeding, cage cleaning) is provided during the isolation period to prevent excessive exposure to personnel. Only medications that can be mixed in the cat’s food will be administered. There can be no exceptions to this policy for radiation safety reasons. Cats that are medically unstable and require daily medical support are not candidates for this type of therapy.

Radioiodine kills thyroid tumors over time; most cats go back to normal thyroid hormone levels within a couple of weeks, but it can take up to 6 months.

Your cat will continue to emit a minimal, but detectable, level of radiation at the time of discharge. This low level of radiation is considered safe by the State of Texas Department of State Health Services. In fact, most people who receive the same kind of treatment are sent home the same day of treatment with no major restrictions. However, in an attempt to minimize radiation exposure to all people to a level as low as reasonably achievable, we recommend that direct contact with your cat be minimized during the first two weeks following treatment. Prolonged contact such as the cat sleeping on your bed or sitting for a long period in your lap is discouraged. We also require that your cat not have close contact with children or pregnant women during this period. Your cat is free to interact with your other pets. At the time of release of your cat from the hospital, you will be asked to sign a paper indicating your understanding of, and agreement to, these precautionary procedures.

All the noticeable effects of radioiodine treatment are good ones, with a few exceptions. Most cats return to normal thyroid function within days of treatment, many being normal by the time of release from the hospital. With normally functioning thyroid glands, the clinical signs of hyperthyroidism (weight loss, hyperactivity, vomiting, skin disease, heart disease, etc.) will slowly disappear. Assuming no other medical problems, your cat should return to a normal state of health.

In a small percentage of cats, thyroid function may become lower than normal. These cats usually show no signs of this condition, but daily hormone supplementation is required.

Though unlikely, it is possible that no measurable response to therapy will be seen and thyroid hormone blood levels will remain high. In some cases, no obvious reason is determined, however; a common cause for this lack of response is the presence of thyroid cancer. While every attempt is made to detect thyroid cancer before treatment, this is not possible

in all cases. Cats with this condition require more extensive treatment.

Many cats referred to us for radioiodine therapy are currently or have previously been given anti-thyroid drugs. Prior to treatment with radioiodine, your cat will undergo a thyroid scan to confirm the diagnosis and better assess the thyroid gland. Tapazole© can alter the result of this scan. In addition, anti-thyroid drugs are known to decrease the radiation dose to the thyroid gland. For these reasons, if your cat is relatively stable without Tapazole©, you should discontinue treatment two weeks prior to your appointment at CATT. However, if your cat requires Tapazole in order to maintain medical stability, you should not discontinue the drug.

Simply fill out our contact form and our team will call you within 24-48 hours to discuss your cat’s history and set up an appointment. Before we can administer treatment, we will schedule your cat to see us for a diagnostic appointment. At this visit, your cat’s thyroid to be imaged with our nuclear scintigraphy camera, creating pictures that our radiologists will use to determine if your cat is a good candidate for treatment, then to accurately plan the location and dosage of I-131. If your cat is a good candidate for treatment, we will schedule a treatment appointment for the following week (depending on availability). You will drop off your cat for treatment and they will stay with us in our cat condo treatment ward for up to three days. The length of their stay depends on how quickly they reach safe radiation levels, which we will precisely measure as required by Texas state regulations.

They will stay with us in our treatment ward for up to three days. The length of their stay depends on how quickly they reach safe radiation levels, which we will precisely measure as required by Texas state regulations. The rate at which your cat reaches safe levels can depend on several factors including the dose (amount) of I-131 that was used. We will provide an estimate during scheduling, and we will update you regularly on your cat’s progress, but please understand that we cannot provide a guaranteed date or time of discharge…only an estimate.

No, the follow-up blood tests to check thyroid hormone levels can be done by your primary veterinarian.