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Radio-iodine treatment for feline hyperthyroidism

Hypertyroidism Animal Accident & Emergency

What is hyperthyroidism?

Hyperthyroidism is a common condition of older cats resulting from excessive amounts thyroid hormone in the blood stream.  The majority of cats will have a benign thyroid tumour causing this condition but some may have a thyroid cancer.  The excessive thyroid hormone in the body speeds up the metabolic rate resulting in the common clinical signs of weight loss, increased appetite and thirst, increased activity and excitability, vomiting and diarrhoea.  A large thyroid gland, increased heart rate, presence of a heart murmur and increased blood pressure may be reported from the physical examination.  The diagnosis is usually made by means of a blood test although sometimes additional testing is required.


How can it be treated?

There are three methods of treatment in Australia: daily medical treatment at home for life, radio-iodine therapy or surgery.  Daily medical treatment will be suitable for some cats but it will not cure the condition and periodic examinations together with blood tests will be required to monitor the cat whilst it is being medicated.  Some cats may not be able to tolerate the drugs used to prevent thyroid hormone production due to side effects and other treatment options will be recommended instead.  Radio-iodine is a simple, effective (over 95% of cats treated will have normal thyroid function after a single treatment) and usually single treatment.  Whilst administration of radio-iodine does require sedation and hospitalisation (at a special licenced facility to allow the radiation to decay), the risk associated with this treatment is low.  Hyperthyroidism may alternatively be treated by surgery to remove the affected thyroid gland (thyroidectomy).  This will require a general anaesthetic and there can be complications following the surgery.

Each cat treated with radio-iodine (or thyroidectomy) will need to be assessed for the presence of other illnesses before the treatment goes ahead.  This is to make sure that there will not be any complications either during the administration of radio-iodine, during surgery or later when the thyroid hormone has decreased to normal.  Both radio-iodine therapy and thyroidectomy provide a non-reversible treatment and one consequence of reducing the thyroid hormone to normal in the blood stream is that for some cats kidney disease may become unmasked by this process.  Those cats which will suffer kidney disease when their hyperthyroidism is treated cannot be predicted from initial blood and urine tests.  This is why many veterinarians will suggest a medical treatment trial (where possible) to reduce the thyroid hormone to normal.  When the thyroid hormone has reduced to normal, blood and urine tests are used to assess how well the kidneys are working.  If the kidneys are not working properly, recommendations will be made depending on the severity of the decreased function.  For some cats this may mean that radio-iodine and surgery are not recommended.  Alternatively, it may mean that the radio-iodine treatment or surgery is postponed while the medication is continued and the kidney function is regularly checked.


What will happen to my cat during the treatment?

Typically, our cats will be admitted on a Monday (before 12 noon) for treatment the following day.  Food is taken out of the cage later in the evening and water is left for the cats to drink overnight.  Sedation is given on the Tuesday to administer the radio-iodine capsule by mouth.  Even if your cat is good at taking medications, sedation will be used to reduce the risk of radiation spillage should the cat not swallow the capsule.  There are strict laws that govern the handling of radiation in Australia.  Administration of the capsule is done in a designated area of our hospital where our patients are then housed during their stay.  Their body is scanned by a Geiger counter to ensure that the capsule has been swallowed properly.  The radiation needs to reduce (decay) to a certain amount and this will usually take a week.  Owners are not able to visit their cats whilst hospitalised due to radiation safety regulations.  During this period, the cats are observed frequently and fed twice daily.  Whilst we provide high quality cat food, some cats may become fussy eaters away from home and we encourage owners to provide a small supply of their favourite food so that their cat may be tempted to eat if they do not enjoy the food offered.  Similarly, we provide bedding but if bedding is provided from home it cannot be returned.


What do I need to do when my cat returns home?

There will be some residual radiation in the cat’s body and prolonged close contact should be avoided for the first week that the cat is home.  This means that your cat may not sleep on the bed with anyone at night or on their laps or be held for periods that exceed 30 minutes per day.  Any pregnant women or children should not have any contact with the cat for the first week that it is home.

The radiation does not work immediately and you may not notice too much difference in your cat’s health at first when they return home.  The radiation continues to works it effect over the next weeks to months and we therefore suggest that a blood sample is collected one month after treatment to assess the response.  This may be taken at our clinic or by your referring veterinarian.

If you are concerned regarding your cats health once home, please do not hesitate to contact our clinic.


Essendon Fields (03) 9379 0700

Point Cook (03) 8368 7400


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