What is Hyperthyroidism?
Hyperthyroidism is a common disorder affecting older cats, caused by the overproduction of thyroid hormones. Like people, cats have two thyroid glands on either side of the neck.
Thyroid hormones are responsible for many processes in the body, so cats may display various clinical symptoms. These can be dramatic in some cats and as a result, cats can become very unwell. If left untreated, it can put your cat's organs including the heart under a lot of strain, leading to organ damage and heart disease/failure.
Clinical signs:
- Weight loss
- Increased appetite
- Vocalising/behavioural changes
- Poor hair coat or coat changes
- Diarrhoea or vomiting
- Increased drinking
- Goitre – increased thyroid gland in the neck
Less commonly, owners might notice that their cats are panting, listless, having difficulty breathing, eating little, behaving oddly, or seeking cool places.
Causes
Most of our hyperthyroid patients are affected by benign nodular hyperplasia, whilst a very low percentage of cats have a cancerous tumour of the gland known as an adenocarcinoma.
Diagnosing hyperthyroidism
If the clinical signs and history fit, your vet will carry out a blood test to check the thyroid level. As hyperthyroidism is a disease affecting older cats, this could mean they have other problems including kidney disease or heart disease. The vet will usually check the kidney parameters at the same time as the thyroid blood test and throughout management of the disease. Blood pressure and heart investigations may also be required.
The good news is the disease is treatable and there are many different options available to do this, including:
- Medication: in the form of tablet, liquid or transdermal gel applied to the ear pinna (off licence product). If your cat is easy to medicate this can be a good option. Side effects can include vomiting, rashes, loss of appetite and sometimes blood abnormalities.
- Food: a special diet called Hills Y/D. This is low in iodine so thyroid hormones cannot be produced. However, if your cat eats any other food whilst on this diet, it will make this treatment ineffective.
- Surgery: to remove an abnormal thyroid gland. This can be a permanent cure but does require a general anaesthetic. In some cats both thyroid glands are affected, and the hyperthyroidism can return. Some cats also have thyroid tissue in their chest that is not easily accessible by surgery.
- Radioiodine: Iodine is used to make thyroid hormone, and iodine that is radioactive destroys abnormal thyroid cells. This is an extremely effective treatment (around 95% of cats respond to a single dose) that resolves hyperthyroidism quickly and painlessly. The iodine can be injected under the skin in the scruff of the neck (just like a vaccine) or given as an oral capsule.
The drawback is that cats must spend time in an isolation facility (up to 2 weeks) while eliminating almost all of the radioactivity from the body before returning home. Owners cannot visit in this time period.
Radioiodine
We are delighted that we have our own Radioiodine Unit at Forest Veterinary Centre, Windsor Place, Harlow, Essex. Dr Alexandra Shutes our Lead Vet at Harlow and our Registered Veterinary Nurse Sharon Hasty supervise the unit on a daily basis and every effort is made to reduce the risk of complications or problems while your cat is with us.
Radioiodine treatment is given via an oral capsule which your cat swallows whilst lightly sedated. Your cat will stay with us for 14 days after treatment is given and will need to stay indoors for up to two weeks once they return home. Daily updates are provided while the cats are in the unit. Radioiodine treatment costs £2,500 including VAT but excluding any pre and post treatment tests.
If your cat meets the following criteria and you would like to enquire about Radioioidine treatment please speak to your vet about a referral:
- Your cat must have a high thyroid hormone concentration confirmed by your Vet.
- Your cat’s general health must be good. If there are any underlying illnesses, they should be discussed with your vet and our referral team. Due to the nature of the treatment, radiation exposure to our nurses and vets must be minimised. Therefore, whilst your cat is in the unit, we cannot handle them, which includes grooming and treating them if they were to become ill. While medications may be placed in food, they cannot be given directly into the mouth. Therefore, if your cat has significant medical problems other than hyperthyroidism, they may not be suitable for this treatment.
- Your cat must be reasonably well behaved. We understand cats with hyperthyroidism can be irritable and show behavioural changes, but we cannot treat cats who may be aggressive as we care for them.
- A blood test should be completed to check kidney function when the hyperthyroidism is well controlled with medication, no more than 1-3 months prior to treatment with radioactive iodine.
- Your cat will require a short heart scan prior to admission especially if they have a murmur or gallop rhythm on clinical exam – this can be discussed with your vet. We can offer this scan as a referral service but this would need to be performed a minimum of 2 weeks before admission.
- Tablets controlling thyroid hormone levels or the Y/D diet should be stopped two weeks before your cat’s admission appointment with us.
- A final blood test to check the thyroid levels will be required one week before admission.
- Your cat must be up to date with vaccinations for cat flu and not showing any signs of potential flu.
