Hyperthyroidism In Cats

What is hyperthyroidism and who does it effect?

Hyperthyroidism is due to an overactive thyroid gland. This may be due to a benign mass or very rarely a malignant mass in the thyroid gland(s). The thyroid glands control an animals metabolism. Many cats over the age of 8 develop hyperthroidism which increases their metabolic rate.

What are the signs of hyperthyroidism?

Because the metabolic rate is increased this will lead to cats eating more, often ravenously, and losing weight, cats may also be restless and hyperactive. Cats may also be drinking and urinating more, some have vomiting and diarrhoea and they may have coat changes (patchy hair loss and matted fur). Many of these cats also develop heart problems and have high blood pressure. Some cats will have a noticeable lump (goitre) in the neck. In advanced cases there may be lethargy and anorexia (loss of appetite).

How does the vet diagnose hyperthyroidism?

A simple in-house blood test can help to identify these cats, we would also recommend testing for concurrent illnesses such as kidney problems and diabetes mellitus which can have many of the same symptoms.

How is hyperthyroidism treated?

There are three treatment options available for hyperthyroidism. Medication, either given orally (tablet) or transdermally (paste rubbed onto the skin) is available & this is given twice daily for life. Surgical removal of the thyroid gland is another option and we can also now offer radioactive iodine (I131)treatment.
We are pleased to announce that we are now one of only two clinics in South Australia licensed to administer radioactive iodine for the treatment of hyperthyroidism in cats. This is the definitive treatment for hyperthyroidism and involves giving a one off dose of radio-active iodine by mouth. There is more information elsewhere on the website relating to I131 treatment (click here).
If your cat has high blood pressure the may need medication for that also.

What is the prognosis for hyperthyroid cats?

The prognosis depends on many factors including the presence of concurrent disease, especially renal (kidney) insufficiency.. Many cats do well on lifelong medical treatment if the owner is able to medicate them easily. Surgery and I131 offer the potential to cure the disease with no ongoing medical requirements. Rarely hyperthyroidism may recur months or sometimes years after surgery or I131 treatment.