Radioactive Iodine Treatment
Understanding Hyperthyroidism in cats
Hyperthyroidism is a common condition affecting middle-aged to older cats. It occurs when the thyroid gland produces too much thyroid hormone, which plays a key role in regulating the body’s metabolism. When hormone levels are too high, it can lead to a range of symptoms and health concerns.
In most cases—over 95%—hyperthyroidism is caused by a non-cancerous condition, either excessive growth (hyperplasia) of the thyroid tissue or a benign tumor (adenoma). Both thyroid glands are usually affected, though one may be more enlarged than the other. The exact cause of these changes isn’t fully understood, but factors such as genetics, diet, environmental influences, and the immune system are likely to play a role.
In rare instances, hyperthyroidism is caused by a malignant (cancerous) tumor known as a thyroid adenocarcinoma.
Clinical signs of hyperthyroidism are usually subtle at first, and get more severe as the disease progresses. The most characteristic signs are:
- Weight loss
- Increased appetite
- Hyperactivity and restlessness
- Increased heart rate (tachycardia)
- Increased urination and/or thirst
- Vomiting or diarrhoea
- Behaviour changes
In advanced cases, your cat could become lethargic and weak and lose his/her appetite.
Once hyperthyroidism is suspected, your veterinarian will perform a thorough physical exam and order a comprehensive blood screen to check their overall health status and thyroid hormone levels to confirm the diagnosis.
During the physical exam, the thyroid gland may be felt as a small, soft mass on either side of the neck. However, it can be challenging to detect, as the glands are mobile and can move along or behind the trachea. In some cases, the thyroid may not be palpable at all.
In rare instances, a cat may exhibit all the signs of hyperthyroidism but have normal thyroid hormone levels. If this occurs, your vet may recommend additional testing. Typically, repeating the thyroid hormone test at a later time is sufficient.
Additional testing can sometimes be necessary. Yor veterinarian will discuss these with you as required.
There are several treatment options available for managing hyperthyroidism in cats, including:
Diet – Hills Prescription y/d can manage thyroid health by reducing excess thyroid hormone production by limiting the amount of ingested iodine, controlling phosphorus and reducing sodium. Packed with L-carnitine, omega 3s and 6s to help with healthy skin, coat and body condition. For this to be effective it must be used as the cat’s sole diet.
Medication – Prescription medication such as Carbimazole and Methimazole reduces the amount of thyroid hormone produced by blocking the way the body processes iodine. There are various forms of administration in the way of tablets, liquid suspension and transdermal gel. Regular blood tests are required ongoing to ensure adequate dosing.
Surgical thyroidectomy – the removal of the thyroid gland/s can be a permanent cure for hyperthyroidism. This method carries significant risks, including surgical complications and development of other endocrine issues (hypoparathyroidism). It has become much less common since the advent of modern medications and especially radioactive iodine
Radioactive Iodine (I-131) – This is regarded as the best method for treating hyperthyroidism. A highly effective treatment that targets and destroys overactive thyroid tissue is commonly used to treat hyperthyroidism. The cat is given a dose of Radioactive Iodine, which is absorbed by the thyroid gland. The radiation from the iodine selectively targets and destroys the overactive thyroid tissue, reducing the production of thyroid hormones. This helps bring the cat’s thyroid levels back to normal.
The aim of this treatment is to eliminate the overactive thyroid tissue that’s producing excess thyroid hormones. Because the thyroid gland naturally absorbs iodine from the bloodstream to make hormones, I-131 takes advantage of this process. The radioactive iodine is administered as an oral capsule, and once absorbed, it is taken up primarily by the abnormal thyroid cells. The radiation then selectively destroys the overactive tissue, reducing hormone production.
Each cat’s dose is tailored individually, based on the severity of symptoms and thyroid hormone levels. Unlike medication or iodine-restricted diets, radioiodine treatment can provide a permanent cure, with over 95% of cats needing only a single treatment. Most cats achieve normal thyroid levels within 4 weeks, although in some cases, it may take up to 6 months for full effect.
Radioiodine therapy is very safe, minimally invasive (only requiring light sedation), and has no significant side effects. Its main drawback is that it involves handling a radioactive substance, so it must be performed at a licensed facility. Treated cats need to stay in the hospital for 7 days, followed by two weeks of special care at home to ensure safe handling.
Overall, I-131 is a highly effective and low-risk option that eliminates the need for long-term medication or dietary restrictions.
Radioactive iodine (I-131) treatment is generally safe and effective for cats with hyperthyroidism, but like any medical treatment, it can have some mild side effects which are usually temporary.
Less Common but Possible Side Effects:
Hypothyroidism (underactive thyroid): In some cases, the thyroid can become underactive after treatment. This may require thyroid hormone supplementation, though in many cats it resolves on its own or doesn’t cause symptoms.
Kidney issues: If kidney disease was masked by the high thyroid hormone levels, it may become more apparent after treatment. This isn’t caused by the iodine but unmasked by the drop in thyroid hormone.
Persistent hyperthyroidism: Rarely, the treatment may not fully resolve the overactive thyroid, and a second dose may be needed.
Cat’s are treated in our hospital on a Tuesday morning and are then hospitalised for 1 week in our nuclear medicine ward. The cost of treatment is $1950 all inclusive of the admission consultation, Sedation, administration of the capsule, monitoring while under sedation, hospitalisation, all meals and bedding, regular monitoring and discharge consultation. We also call or SMS owners every evening with updates for peace of mind. Feliway is used in the wards to reduce anxiety and we endeavor to customise bedding requirements to ensure a comfortable stay.
To begin, we require a referral from your veterinary clinic, including your cat’s relevant medical history, all bloodwork since diagnosis, and a recent urine test. Once we’ve received this information, our veterinarians will assess your cat’s suitability for Radioactive Iodine Treatment. This assessment can take up to a couple of weeks and may occasionally require additional testing or treatment at your regular vet before moving forward.
At this stage, communication typically occurs between our team and your vet. Once your cat is approved for treatment, either we or your referring clinic will contact you to arrange a booking. Treatment days are scheduled on Tuesdays.
After your booking is confirmed, we’ll send you an information sheet and a consent form, which we ask you to review and complete before admission. An invoice covering the treatment and hospitalisation will also be sent, with full payment due by the Thursday prior to your appointment.
Your cat will be admitted to the hospital by one of our vets or vet nurses. When it’s time to administer the capsule, a light sedation is given to ensure it can be safely delivered. While your cat is sedated, we check their heart rate, blood pressure, and thyroid glands, and we also clip their nails. They are then moved to their suite, where the capsule is administered orally with a small amount of water, and they are settled in to recover. Once they have fully woken from sedation, we make sure they’re comfortable and set up their bedding for the week ahead.
A capsule of Radioactive Iodine was administered 7 days ago, and the level of radioactivity emitted is now relatively low. To further reduce the risk from the radiation it is important to follow the instructions detailed below for the next two weeks;
- Wash hands after handling.
- Avoid long periods (more than half an hour) in close proximity with your cat, particularly during the first week. It is safe to pick them up for short periods but they should not sit on anyone’s knee for extended periods or sleep next to them on a bed.
- Take particular care if handling any urine. If your cat uses a litter tray then place tray in an unoccupied area. When changing the litter tray wear a pair of rubber gloves used specifically for this purpose and wash your hands very thoroughly afterwards. Carefully empty the soiled litter into a rubbish bag and wash the litter tray thoroughly.
- If your cat accidentally urinates inside the house, the urine should be cleaned up thoroughly with paper towels (remember to wear gloves) which are then placed in a rubbish bag. If the urine has soaked into garments or carpets they should be washed and cleaned thoroughly. Dilution of the urine is important. The rubbish bags may be disposed of in the normal manner. It is of no concern if your cat urinates in the garden and no special precautions need to be taken.
- Keep your cat away from any area where human foodstuffs are stored, prepared or consumed. (Such as the kitchen bench).
To assist recovery the following care is essential:
Ensure your cat is kept comfortable and quiet for the next 14 days.
Ensure fluids are available and offer normal meals.
Please contact your regular veterinarian IMMEDIATELY if you notice any of the following:
Your cat is not acting normally, refuses food or fluids or seems to be uncomfortable.
Symptoms of hyperthyroidism typically take up to 4 weeks to dissipate. We recommend a follow-up blood test with your regular vet at this time to monitor the thyroid levels post treatment. Often, they are within the normal reference range at this time.
Can my cat interact with my other pets when they get home?
Yes, they can interact as normal with other pets in the household
Can I supply bedding from home for my cat?
Of course, we encourage something that smells of home throughout their visit with us. Please keep in mind that any bedding or toys that go into the ward cannot be sent home, so please make sure it is something you will not miss.
What if my cat has special dietary or medication requirements?
Please let us know before booking if your cat has any medication that will need to be given while in our care. In most cases we are able to administer as required.
We feed hospitalised cats Hills Prescription i/d dry food, we also have a variety of wet food options available. If your cat has specific dietary requirements, please bring any special food with you upon admission.
Can my cat interact with my children when they get home?
Young children and pregnant women are advised to avoid any contact with their cat for 2 weeks after discharge from our hospital. After that time, you can all interact together as normal.