Hyperthyroidism in Cats

What is feline hyperthyroidism?

Feline hyperthyroidism is the most common endocrine (hormonal) disorder of cats. It is an older cat disease. Though it has been recorded in cats as young as 4 years of age, it is uncommon in cats under 8 years of age. It is a syndrome caused by the increased secretion of thyroid hormone. This is usually due to a benign tumour of the gland. In 2% of cases it may be a malignant tumour that can spread to other organs. One survey (in England) puts the incidence of hyperthyroidism as 10% in cats over 10 years of age.

Clinical signs of feline hyperthyroidism

It is a multi-systemic disease. This means that it affects many body organs, and organ systems, as such; hyperthyroidism can clinically look similar to many other conditions (e.g. renal failure).

The most common clinical signs are weight loss and increased appetite. Other signs include:

  • hyperexcitability or anxiety
  • palpable goitre (gland can be felt in the neck)
  • gastrointestinal signs(vomiting or diarrhoea)
  • rapid heart rate/thumping heart
  • signs of congestive heart failure
  • fluid retention in chest and abdomen (relates to heart symptoms)
  • increased drinking and urination
  • some cats have alternating periods of decreased and appetite

Diagnosis of feline hyperthyroidism

Diagnosis is via a blood test. The level of thyroid hormone is measured in the serum. A general blood test for the liver and kidney function can also be useful.

Treating  feline hyperthyroidism

There are three treatment options:

1. Radioactive iodine treatment

This is only available through specialist centres. The cat is given a capsule containing radioactive iodine, which is taken up into the gland and kills the gland tissue. It is a very safe and effective treatment, but it involves a stay in hospital in a special lead-lined room until the level of radioactivity in the cat is deemed safe – usually 7- 10 days.

2. Surgical

Despite most hyperthyroid cats being quite old and despite there being some increased anaesthetic risk, if care is taken, surgery usually gives very dramatic results. There is no need for an extended stay in hospital, and the cost for this treatment is usually less than for radioactive iodine treatment. However, this is only useful for those cats with an enlarged thyroid gland.

3. Medical

Adequate in the short term, or as a preparation for surgery, but not as successful in long-term management. Some patients with other health problems such as diabetes or kidney failure may be best treated this way.

The outlook for most cats with thyroid disease is very good, so prompt identification and treatment of the problem will rapidly improve your cat’s quality of life.


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