Radioiodine treatment for cats
Did you know that an overactive thyroid gland (hyperthyroidism) is a serious problem prevalent in cats over 10 years of age?
Common signs of hyperthyroidism include vomiting, an increased appetite, changes in behaviour and weight loss. It can also bring about serious secondary complications like heart disease. It’s a life-threatening condition, but thankfully it’s treatable in all cases and curable in the majority of cases.
There are several therapies for the management of hyperthyroidism but radioiodine treatment is considered the gold standard. Not only is it a highly effective treatment, but it has few, if any, side effects and is administered with a single oral capsule. It’s the same treatment used for humans suffering hyperthyroidism.
What is involved in radioiodine treatment for cats?
Pre-treatment consultations
Consultations for assessing cats are needed before treatment can start. Your cat and its medical history will be assessed at the time of the consultation to determine if it is a suitable candidate for radioiodine treatment and the radioactive iodine dose will be determined.
It is unlikely that treatment will be administered on the same day as the consult, but your cat may be admitted to hospital on the same day. Please contact our Client Services team for more information around hospital admission processes.
Thyroid medication before an appointment
For cats with mild to moderate hyperthyroidism, discontinue anti-thyroid medications and Y/D diets at least 5 days prior to your cat’s appointment for radioiodine treatment.
A small number of cats have severe clinical signs from their hyperthyroidism where it would be dangerous to discontinue the medication. This applies to cats with severe, chronic, poorly controlled hyperthyroidism or cats with heart and respiratory complications or who are weak. In these cats, we can only discontinue medication for a short period before radioactive iodine treatment. If you and your veterinarian feel that the cat’s hyperthyroidism is too severe to stop medication, please have your veterinarian contact us to discuss other options.
If you have any questions, please contact your regular veterinarian. If your veterinarian needs further assistance, they may reach out to our Internal Medicine service for advice. Communication will be through your regular vet until we have met you and examined your cat.
Giving the treatment
Cats are usually assessed on Monday, any necessary new laboratory results are received on Tuesday, and treatment is administered on Wednesday. This timeline ensures that cats are eating, drinking, and stable in the hospital before being transferred to the relative isolation of the radioactive iodine ward.
Hospitalisation
After treatment, patients must be housed in our radioiodine ward and have their health and welfare monitored each day to ensure radioactive emissions have dropped to a suitable level. Due to strict safety regulations, you won’t be permitted to visit your cat for the duration of hospitalisation.
While they are with us, handling by the SASH team is also restricted. Grooming is not possible, and medications can only be placed in food, not administered directly. Cats with significant medical issues, besides hyperthyroidism, may not be suitable for this treatment as we cannot administer treatments without exposing hospital staff to high levels of radioactivity.
For your safety, cats are hospitalised for a minimum of 5 days and until their radiation levels are below a safe level. This usually takes between 5 and 7 days.
Follow up
Recheck appointments should occur at 6 weeks, 6 months, and then yearly. For cats with complicated medical history we may recommend more frequent rechecks.
Each consultation should include a complete physical examination (including a blood pressure reading) and blood tests. In general, the laboratory testing to perform at these times include a serum chemistry panel, including creatinine (kidney function tests) and a serum thyroid testing (T4 and TSH concentrations). The thyroid tests should be sent to an external laboratory.
Cats with kidney disease and hypothyroidism after treatment often require treatment with thyroxine (a thyroid supplement). This is usually a short-term treatment but can be long term in a small number of cats.
You are very welcome to return to SASH for these follow-up tests, but many owners prefer to consult with their local referring veterinarian. In these cases, communication regarding the test results will be through your referring veterinarian. However, your veterinarian is able to contact the SASH Internal Medicine team for advice.
Efficacy of radioiodine for cats
Most hyperthyroid cats have a benign thyroid tumour that absorbs radioactive iodine during treatment. Studies indicate that approximately 95% of hyperthyroid cats are permanently cured with a single treatment. The remaining normal thyroid tissue will return to function within 3 to 6 months. Cats that are not cured often show clinical improvement due to reduced thyroid hormone levels. If your cat isn’t cured within 3 to 6 months, retreatment with radioiodine is recommended.
Higher doses of radioactive iodine can cure more hyperthyroid cats but also increase the risk of hypothyroidism. We aim to give each cat an individualised dose that destroys the thyroid tumour while preserving normal thyroid tissue. However, some cats may still develop hypothyroidism which requires close monitoring and possible hormone supplementation. Most cats do not show signs of hypothyroidism, so this is diagnosed by follow up blood tests. The main concern with hypothyroidism is that it exacerbates underlying chronic kidney disease.
Recurrence of hyperthyroidism is uncommon (less than 5% of treated cats) and are usually due to a new thyroid tumour.
If you are worried that your cat may have hyperthyroidism, please see your local vet to have them checked. If your cat has hyperthyroidism, ask your vet about radioactive iodine treatment or contact our team by clicking the button below.
Hyperthyroidism and kidney disease
Older cats often suffer from hyperthyroidism and chronic kidney disease (CKD), with some affected by both. Hyperthyroidism masks CKD by making the kidneys work harder, rendering blood tests unreliable for assessing kidney function. Treatment for hyperthyroidism can reveal pre-existing CKD. Fortunately, the prognosis is good for cats whose CKD is unmasked, as long as they do have concurrent hypothyroidism.
Safety of radioiodine for cats
Radioactive iodine will naturally decay giving off gamma rays (like X-rays) and beta particles (electrons). The half-life of I-131 is 8 days. In other words, one-half of the radioiodine decays every 8 days. After discharge, your cat will still be minimally radioactive. Even though the level of radioactivity is low you should still exercise the following safety precautions for two weeks after discharge:
- Protect yourself and your family by avoiding close and prolonged contact with your cat. ie close contact should be brief, prolonged contact should be at least one large stride away from the cat
- Your cat may not be on your bed while you sleep.
- Your cat should not be near children or pregnant women.
Most of the radiation will be excreted in your pet’s urine. You should scoop the litter box at least once or twice a day and remove urine soaked litter from the house or apartment. You should wear gloves gloves when changing the litter and wash your hands after handling.
The amount of radiation that your other pets will receive by contact with your cat or by using the litter box is negligible. If you have multiple cats sharing the same litter box, however, we do recommend that you clean the box at least once a day to remove the contaminated litter clumps from the box.