Hyperthyroidism in Cats
What is hyperthyroidism and what causes it?
The thyroid gland is responsible for the production of thyroid hormones. In hyperthyroidism
the thyroid gland produces more thyroid hormone than normal. In the majority of cases the
increased production of thyroid hormones is due to a benign tumour of the thyroid gland. In
a small minority of cats (1-3%) the increased production can be due to a malignant tumour
of the thyroid gland.
Hyperthyroidism is the most common endocrine disorder in cats. The reason for this is not
known but it is thought that it may be linked to feeding tinned foods, the use of cat litter
and certain chemical products such as insecticides. However, there has yet to be a firm link
made between these risk factors and the disease.
What are the symptoms of hyperthyroidism?
Below is a list of common symptoms associated
with hyperthyroidism
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Vomiting
Weight loss
Increased appetite
Increased thirst and urination
Erratic behaviour
How is hyperthyroidism diagnosed?
If we suspect your cat has hyperthyroidism we will first carry out a routine blood test to
check your cat’s overall health. This will enable us to rule out other underlying illnesses that
may have similar symptoms. If we still suspect your cat is suffering from hyperthyroidism
then we will perform one or several blood tests to check your cat’s thyroid hormone levels.
This enables us to confirm the disease and will help with deciding on the best treatment
option.
How is hyperthyroidism treated?
There are three main ways in which hyperthyroidism can be treated
1. Medically with the use of daily tablets
2. Surgically, involving removal of the diseased thyroid tissue
3. Radioactive iodine, a treatment designed to target only the diseased thyroid tissue
All three of these options have pro’s and con’s. The treatment that may be most
appropriate for one cat may not be suitable for another. For this reason, these treatment
options will be discussed with you by the vet at the time of diagnosis. In the majority of
cases, cats are started on oral medication. This enables the condition to be stabilised and is
often a safer initial treatment option in elderly cats that would not be suitable for an
anaesthetic (for surgery) or long periods of hospitalisation (for radioactive iodine).
How will the disease progress?
After the initial diagnosis we advise rechecking your
cat’s thyroid levels at 3, 5 and 8 weeks after the start
of medication. This will enable us to ensure we are
giving your cat the correct dose to keep his/her
symptoms under control. It is also important to
recheck your cat’s blood cell levels and organ
function on starting medication as occasionally we
find that other diseases can become ‘unmasked’ such
as kidney disease on starting medication. The blood
tests will also enable us to monitor for any sideeffects of the medication such as low cell counts and liver problems.
The length of time your cat will live for after diagnosis largely depends on the underlying
cause of the disease and how well the disease is controlled. If not fully controlled, the
disease can go on to cause other illness such as heart disease and hence it is important that
we recheck your cat on a regular basis. Once your cat’s condition is stable we would
recommend a re-visit and repeat blood tests every 3 months.
The Swanbridge Veterinary Group, Tranby Lane, Swanland, HU143NG.
Tel: 01482 633888, Fax: 01482 634 576, Email: info@swanbridgevets.com