The thyroid gland produces thyroid hormones which are responsible for regulating the body’s metabolic rate. An excess of the thyroid hormone ‘thyroxine’ or T4 is referred to as hyperthyroidism.
Hyperthyroidism is caused by a tumour or lump within the thyroid gland which, although often tiny and difficult to locate, results in the excessive production of thyroid hormones.This causes many different effects within the body. Fortunately, 97% of these tumours are benign.
Hyperthyroidism is a disease often found in cats over the age of 10 years of age. It was first brought to the attention of veterinarians in the USA in 1979. Since then it has been diagnosed in many countries throughout the world and has been recognised in Australia since 1980.Over the years the frequency of hyperthyroidism has increased in numbers.
Too much thyroid hormone results in the signs that you may have seen in your cat:
- increased appetite
- weight loss
- increased drinking and urination
- restlessness and vocalisation
- gastrointestinal upset
- rough hair coat
Many of these older cats also have other concurrent diseases, e.g. heart, liver or kidney disease. These diseases may have an impact on the way that the cat is treated.
The onset of symptoms is usually insidious and may mimic other diseases that are seen in older cats which both owners and veterinarians alike may not recognise as thyroid disease until it is in quite an advanced stage. The original symptoms usually include a weight loss in spite of a good appetite. As the disease progresses the cats tend to become more and more demanding of food. They may have temperament changes and become more nervy and jumpy. Sometimes they become very vocal and demanding of attention. Often their thirst will increase, they are prone to gastrointestinal upsets as they cannot digest their food properly and their coats become rough.
A full blood screen should be performed on your cat before treatment is commenced.
Death from this disease is usually due to cardiac failure.
Despite some investigation principally carried out in the U.S.A. but also at GVH where we have been involved in two research projects, the underlying cause of the disease is still not understood.
In cats where the disease is present in one thyroid gland it is found eventually to affect the second gland in 70% of cases.