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Overactive thyroid disease in cats

It is not just humans that can suffer with thyroid disease.  In cats, the most common thyroid disease we see is hyperthyroidism i.e. an overactive thyroid gland.

Like us, cats produce thyroid hormone in glands in their neck.  Unfortunately in middle-aged and older cats, we see hyperthyroidism fairly commonly.  In most cats this is due to a benign enlargement of the glands, but in rare cases it can be cancerous.  The good news is this condition can be successfully treated in most cats.  It is important to start treatment as early as possible, as if left untreated more serious effects e.g. heart disease, can develop.


The most common symptoms of hyperthyroidism in cats that we see include:

  • Weight loss, despite a normal or increased appetite.  It is important to have your cat weighed regularly e.g. at their annual health check with the vet, as it is sometimes difficult to notice gradual weight loss when you see your cat every day.
  • Drinking more.
  • Unkempt coat.
  • Diarrhoea.
  • Changes in behaviour e.g. yowling more, irritable, unsettled.
  • The vet may also note a rapid heart rate when they examine the cat.

If left untreated serious heart disease or high blood pressure can occur.

How do we diagnose hyperthyroidism?

This is usually a simple disease to diagnose, using a blood test to measure thyroid hormone level.  If a vet suspects hyperthyroidism they will advise a blood test to include thyroid hormone, but will also want to check for other diseases e.g. diabetes and kidney problems that can have similar signs.  Some cats unfortunately can also get more than one disease! Blood pressure and urine tests may also be advised.

Thyroid hormone is included in our older cat nurse screening package. It is advised to screen older cats annually for disease as in the early stages they often will not have any symptoms, but in many cases the earlier we start treatment the better.

How do we treat hyperthyroidism?

Most cats are initially treated with tablets or liquid oral medication.  Some owners choose to continue lifelong medication for their cat; these cats require regular check-ups and blood tests to make sure they are being treated effectively and not suffering any side effects.

It is possible to surgically remove the overactive thyroid gland.  There are two glands in the neck, and it is possible for the second gland to become overactive in the future.

The ‘gold standard’ treatment is referral to a special facility where the cat undergoes radioactive iodine treatment.  This is not as scary as it sounds!

There is also a special diet that can be effective provided the cat isn’t eating other food elsewhere.

The vet will discuss the best option for your cat, taking into account any other health conditions they may have and your own circumstances.

Can I prevent my cat from getting hyperthyroidism?

Unfortunately we don’t yet know why this is such a common condition in pet cats, so there is nothing specific you can do to prevent it.  The best advice is to ensure your cat is getting checked regularly by a vet and to follow the ISFM screening guidelines.  This way we are more likely to pick up problems at an earlier stage with better outcomes.

To book your cat in for a check-up give us a call on 01803 606059 (Torquay) or 843836 (Paignton) or book online.

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