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Thyroid diseases are common in middle-aged to older cats and dogs.
Cats are more prone to getting an ‘over-active’ thyroid gland, whereas dogs are more likely to develop an ‘under-active’ thyroid gland.
The thyroid gland can become diseased and atrophied and eventually lose the ability to produce sufficient levels of the necessary hormones. As a result affected dogs may show signs such as:
Diagnosis of an under-active thyroid (hypothyroidism) is made by measuring specific hormone concentrations in the blood.
Treatment is lifelong, as it involves replacing the hormones that the dog can no longer produce on its own. It’s most commonly given as a small tablet, once a day. Clinical signs often improve within a month of starting treatment but can take several months for the full effect.
Once on treatment and the dog is stable, blood monitoring is recommended every three to six months.
The prognosis following treatment is excellent for most adult hypothyroid dogs.
An over-active thyroid gland in cats leads to a condition known as hyperthyroidism, which is now one of the most common hormonal (endocrine) disorder of cats. The disease is most commonly caused by a benign (non-cancerous) tumour that produces too much of the thyroid hormones.
In less than two per cent of cats the condition may be caused by a malignant cancer. In these cases, cats have a poorer prognosis and are more difficult to manage.
Too much thyroid hormone causes an overactive metabolism and a wide range of clinical signs including:
Hyperthyroidism most commonly affects cats over 8 years old. The cause of the disease is currently unknown.
A simple blood test to check the level of T4 in your cat’s bloodstream can diagnose the disease. Often we will recommend checking kidney function and your cat’s blood pressure at the same time, as hyperthyroidism may affect these.
What treatment is available for hyperthyroid cats?
There are four main treatments available for cats with an overactive thyroid:
