Nov 8, 2017

Hyperthyrodism in Cats

Over-active thyroid glands are a common issue with older cats

Feline Hyperthyroidism

The thyroid glands are two glands that sit in the neck on either side of the windpipe.

Feline hyperthyroidism is normally caused by benign growth of the thyroid glands. It is not known what causes this growth. This results in excessive production of the thyroid hormones, mainly thyroxine (T4).

The disease affects older cats (usually over 10 years) and all breeds of cat can be affected.

Signs your cat may show including:
  • weight loss
  • an increase in appetite
  • hyperactivity
  • unkempt coat
  • a “starey” expression
  • vomiting
  • diarrhoea
  • an increase in thirst and urination

Diagnosing Feline Hyperthyroidism

To help us diagnose feline hyperthyroidism we will take a blood sample from your cat. This will be sent to specialist laboratory where experts will measure the level of thyroid hormone in your cats blood.

A VERY HIGH level of thyroid hormones is diagnostic – your cat has hyperthyroidism

A HIGH level of thyroid hormone is suggestive of the disease but we may need to retest the levels in a few weeks time

A NORMAL or LOW thyroid hormone level can mean two things:
  1. Your cat does not have hyperthyroidism!
  2. If your cat is clinically unwell he may still have hyperthyroidism. Illness can lower the thyroid hormone levels, therefore it may be necessary to retest the thyroid levels once your cat is feeling better


We have three options when it comes to treating hyperthyroidism:

1) Medical Management

This is the most common way we manage the disease. We normally use the drug carbimazole (Vidalta)when treating your cat. We start by giving half or one tablet  once a day, then test the thyroid levels approximately 3 weeks later to see if we need to change the dose. Other options include a paste that can be rubbed on the ear.

2) Surgery

Surgical thyroidectomy (removal of the thyroid gland) is frequently curative but there are risks associated with the surgery. Depending on the individual case either one or both thyroid glands may be removed in a single operation. It is always necessary to stabilise the cat with medical management prior to surgery.

3) Radioactive Iodine Treatment

This is the gold standard treatment for cats that are otherwise healthy. The treatment is safe and effective, and usually curative. However there are downsides: it is expensive, only available at specialist referral centres (such as VSG); involves a long stay in hospital and is not suitable for cats with concurrent illnesses.

5) Hills y/d food

This prescription food manages hyperthyroidism by limiting the level of iodine in the diet. It sounds very easy but it is only suitable for cats that do not eat over at the neighbours – because in order for it to work properly it must be the ONLY food fed to your cat!


We monitor your cats condition in two ways:

1) Regular check ups to see that they are happy and healthy

2) Regular blood tests to check the thyroid hormone levels – these are normally performed at 3 weeks, 6 weeks, and 3 months after diagnosis. Once the thyroid levels are stable we recommend repeating the blood test every 6 months.


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