Hyperthyroidism
GVH is a Referral Centre for Nuclear Medicine in Sydney and Australia-wide.
Our procedure and treatment plans are unique in the Southern Hemisphere! We scan our patients to enable us to give an exact and individual dose for each patient, no other site has the facility to do this. Individual dosing minimizes risks or adverse side effects and allows a better success rate for our patients to go into complete remission. Please contact our team for more detailed information on what we do and how we do this at GVH
The thyroid gland produces thyroid hormones which are responsible for regulating the body’s metabolic rate. An excess of the thyroid hormone ‘thyroxine’ or T4 is referred to as hyperthyroidism.
Hyperthyroidism is caused by a tumour or lump within the thyroid gland which, although often tiny and difficult to locate, results in the excessive production of thyroid hormones. This causes many different effects within the body. Fortunately, 97% of these tumour’s are benign.
Hyperthyroidism is a disease often found in cats over 10 years of age. It was first brought to the attention of veterinarians in the USA in 1979. Since then, it has been diagnosed in many countries throughout the world and has been recognised in Australia since 1980. Over the years the frequency of hyperthyroidism has increased in number.
Too much thyroid hormone results in the signs that you may have seen in your cat:
- increased appetite
- weight loss
- increased drinking and urination
- restlessness and vocalisation
- gastrointestinal upset
- rough hair coat
Many of these older cats also have other concurrent diseases, e.g., heart, liver, or kidney disease. These diseases may have an impact on the way your cat is treated.
The onset of symptoms is usually insidious and may mimic other diseases that are seen in older cats. Both owners and veterinarians alike may not recognise these symptoms as thyroid disease until it is in quite an advanced stage. The original symptoms usually include weight loss despite a good appetite. As the disease progresses the cats tend to become increasingly demanding of food. They may have temperament changes and become nervier and jumpier. Sometimes they become very vocal and demanding of attention. Often their thirst will increase, and they become prone to gastrointestinal upsets as they cannot digest their food properly and their coats become rough.
Despite some investigation principally carried out in the U.S.A. (but also at GVH, where we have been involved in two research projects) the underlying cause of the disease is still not understood.
In cats where the disease is present in one thyroid gland it is found eventually to affect the second gland in 70% of cases.
Treatment Options
There are three common treatment options for feline hyperthyroidism.
- Medication
Drugs are available that reduce thyroid hormone production. However, these do not cure the disease. These drugs often need to be given twice a day for the life of the cat and can have some side effects. These medications should not be given for two weeks prior to radiation therapy. - Surgery
Surgical treatment involves removal of the affected thyroid gland(s). This can provide a cure for the disease. However, due to the age of most cats affected and the possibility of heart disease there is some anesthetic risk involved.
Complications may arise when both glands need to be removed. This occurs when the parathyroid glands are removed with the thyroids. This is a common complication resulting in problems with calcium regulation. - Nuclear Medicine and Radioactive Iodine
The third form of treatment uses nuclear medicine technology and is considered by most experts in this field to be the method of choice for these older cats. It provides a safe and simple cure for hyperthyroidism.
The thyroid gland needs iodine to manufacture thyroid hormone. Advantage can be taken of this to inject an exceedingly small dose of radioactive iodine into the cat. This iodine is then extracted from the blood by the tumour cells and then for them to make more thyroid hormone. The tumour cells are therefore directly exposed to the radiation and therefore die.
The surrounding normal thyroid cells do not tend to take up the radioactive iodine and are spared from the radiation and can subsequently function normally again.
The only real disadvantage to this treatment is that the cats are slightly radioactive for a few days after treatment and must be kept in strict isolation. After this period, the cat can return to their home environment, but we advise owners not to have prolonged close contact with their cats for another 2-3 weeks. We also discourage cats from sleeping on your bed or sitting on someone’s lap in this period.
Protocol for Radioactive Iodine Treatment
A strict protocol is adhered to in all nuclear medicine cases to ensure the safety of your pet, your family, and our staff. We also aim to keep you informed during all stages of the treatment.
Pre-Consultation
At GVH we are passionate about your pet’s safety and best outcome, so we recommend the following pre consultation tests and actions to ensure the best results. All cats need a full blood test, including Biochemistry including SDMA, Hematology and T4, a basic urine test and be up to date with their vaccination (as they must isolate from Monday/Friday in our feline isolation unit alongside other hyperthyroid patients), and flea/tick/worm medication. Your regular Vet can arrange all of this for you, and they can contact us to discuss the results and form a treatment plan
Consultation
Radiation therapy is performed by the Nuclear Medicine Team on Mondays. Therefore, consultations for hyperthyroid cats are held on Monday mornings. During the consultation your cat will be thoroughly examined, their records assessed, and pathology results checked and discussed. Your cat will be admitted into hospital after this consultation.
Sedation
To reduce any anxiety and enable thyroid scanning, all cats are sedated prior to their scan. The drugs used for this purpose are selected to have minimal side effects.
Thyroid Scanning
Before treatment, a small dose of a radioisotope Technetium 99m is given to each cat. Once this has had time to concentrate in the thyroid gland (about 20-30 minutes) a radiation emission scan is taken. The amount of isotope taken up by the gland is used to calculate the therapeutic dose of radioiodine.
Method of Treatment
The radioactive iodine is given as a single injection under the skin. This causes minimal discomfort to the cat during treatment and recovery.
Aftercare
Hospitalisation
After treatment, cats are kept in our isolation ward until their radiation levels are below Government EPA standards. During their stay, they are regularly checked by the in-hospital vet, who will call you daily with an update on your cat’s progress. We try to avoid boarding your cat for longer, as the isolation facility is not very spacious or homely for them, but if you have any concerns about exposure, please contact our team to discuss options to help you
Discharge
Cats are not discharged until their output of radiation is deemed safe, usually after 5 days. For your added safety we recommend not letting your cat sleep on the bed or sit on your lap for another 2-3 weeks. Daily cleaning of litter trays is also important as urine and faeces are the main way in which radiation is excreted. We send out homecare instructions before we arrange your cat’s procedure to make sure you are comfortable with how to manage them at home during this time
Rechecks
Your cat should be rechecked by your regular vet 6-8 weeks (about 2 months) after discharge. This enables them to assess your cat’s progress and check blood tests to ensure that the thyroid hormone level has reduced. You can usually expect your cat’s behaviour to return to normal a month or so after treatment. Although the international recurrence rate of hyperthyroidism in cats is reported to be about 10% of the cats treated at Gladesville, only 0.3% have required subsequent treatment.
Prognosis
Cats treated in this fashion often have developed a normal thyroid function within one week of treatment and have recovered from their disease within 4 to 6 weeks from treatment.
GVH has treated over 3000 cats for hyperthyroidism and routinely continues to treat 4 cats per week. So, rest assured your cat is in experienced hands!