Radioiodine therapy (or radioactive iodine therapy) is a fantastic treatment option for cats with hyperthyroidism. Still, with all treatments, there are pros and cons. If your vet has mentioned this therapy to you for the first time, you are probably trying to decide what to do, and this can be a stressful decision. Understanding your cat’s treatment options and prognosis is crucial in order to make the best decision for your cat and you.

Read on to discover some of the most common questions people have about radioiodine therapy in cats and what you need to consider when making this decision. 

Why has my vet offered radioiodine therapy for my cat?

If your cat is hyperthyroid, it is likely that your vet will mention radioiodine therapy at some point. To understand how radioiodine treatment works, it is important to understand a little about hyperthyroidism too. 

The condition occurs due to a benign growth of extra cells in the thyroid gland, but in rare cases, it can be due to a type of malignant cancer called thyroid carcinoma. These extra cells absorb iodine from the bloodstream and use it to produce more thyroid hormone (thyroxine), which travels around your cat’s body and increases their metabolism. High levels of thyroxine lead to a high metabolic rate, and the body’s normal functions speed up. This may lead to your cat having a rapid heart rate, high blood pressure, anxious disposition, and marked weight loss despite an insatiable appetite. The long-term effects of hyperthyroidism can be very damaging. The disease will affect your cat’s quality of life, so treatment should always be considered.

What is radioiodine therapy?

Radioiodine therapy involves a single injection of radioactive iodine under your pet’s skin. The radioactive iodine will concentrate in your cat’s thyroid gland (just like normal iodine does) but once there will actively kill the abnormal cells that are over-producing thyroid hormone. The radioiodine is gradually eliminated from your cat’s body over the following weeks. However, the majority will be excreted in your cat’s urine rapidly within the first few days. 

What does radioiodine therapy involve?

The treatment can be a daunting prospect, but it is not as scary as it sounds. Radiotherapy for cats can only be performed at specialist centres, to which your vet can refer you. Prior to treatment, the specialist veterinary surgeon will perform a full assessment of your cat, including blood tests and ultrasound. All treatment courses require an extended hospital stay, during which your cat will be emitting radiation, so they cannot be handled by people. Visits are strictly off limits, which can be a real wrench for many owners. But the long-term rewards can be great, and your cat will receive excellent care, so it may well be worth the sacrifice in the short term. Most cats will remain at the facility for 8-12 days. Those cats receiving higher doses of the medication to treat the more aggressive thyroid carcinoma will be hospitalised for much longer.

Once your cat is home, you will be advised regarding further precautions that need to be implemented in the following weeks. This will likely involve keeping your cat indoors, minimising close contact and carefully disposing of their litter tray contents. Some hospitals will offer an optional extended stay if you are worried about this post-treatment period. Occasional blood tests, urinalysis and blood pressure measurements are required to monitor your pet for any future issues. In rare cases, cats develop ongoing hypothyroidism (low thyroid hormone levels) after radioiodine therapy.

Are there any benefits of radioiodine therapy?

Radioiodine therapy can be a fantastic option, here’s why:

1. No need for anaesthesia (unlike surgical options), although sometimes light sedation is required

2. Treatment has a cure rate of over 95% – which are great odds!

3. Side effects are rare

4. It is a real treatment option for thyroid carcinoma

5. It is non-invasive and does not carry the risks, such as bleeding or parathyroid gland damage, that can be caused by surgery

6. It can be repeated if needed in future

Is radioiodine therapy safe for me and my cat?

Understandably, you might have concerns regarding radiation exposure. However, you must remember that we are all continually exposed to environmental radiation. Specialist radioiodine units monitor all exposure in their staff to keep them safe. In contrast, the radiation you might be exposed to is much lower and can be likened to the same levels as a long-haul flight. As a precaution, it is recommended that you limit close contact with your cat for approximately 2-4 weeks following treatment. For pregnant women, children and visitors, contact within 6 feet should be avoided, so setting up a kitty base in a spare room away from the family is a good idea. Radioactive iodine is excreted in urine, saliva and sweat, so you will be advised how to safely clean litter trays and bowls.

As with all treatments, risks are always involved, but these are considered low in feline radiotherapy. There are currently no known side effects associated with the injection of radioactive iodine. Any symptoms observed tend to be associated with fluctuating thyroid hormone levels. In addition, managing hyperthyroidism with any treatment option can unmask underlying kidney disease. Your cat may develop hypothyroidism, but this is transient in most patients and lasts for just a short time following therapy. The detailed pre-treatment screening tests aim to identify other illnesses that might indicate that radiotherapy treatment is unsuitable for your cat.

What other treatment options are there?

Your vet will talk you through all treatment options at your initial consultation. The three other options are:

1. Medical treatment (usually tablets)

2. Prescription diet

3. Surgery (thyroidectomy)

Each of these options carries different success rates, risks and costs. You will need to think carefully about which type suits your cat best; after all, every cat is different, with different personalities and different levels of tolerance for vet visits. But also, you must consider what fits in most effectively with your lifestyle and budget, and consider how you feel about any risks involved. You can read more about hyperthyroidism and the different treatment options here.

Making the best decision for your cat

Radioiodine therapy is not suitable for every cat but, due to its success rate, it is a great option for many. Your vet will help you to decide which treatment options are appropriate, and further checks will be undertaken at the specialist centre. It is worth noting that radioiodine therapy can be costly, so checking your budget is important. However, if your cat’s condition is stable and they tolerate vet visits, treatment with radioactive iodine may be their best bet for a long and happy life.