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:
cold intolerance (seeking heat)
lethargy, tiring on exercise
skin problems (hair loss, hair colour and quality changes, predisposition to skin infections)
abnormalities of the reproductive and nervous systems (less common).
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:
weight loss, despite a healthy (if not increased) appetite
a dull coat in poor condition
abnormal behaviour including vocalisation, restlessness, hyperactivity
sudden onset blindness
dangerously high blood pressure
vomiting and diahrroea.
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:
anti-thyroid medications: these drugs suppress the production of thyroid hormones.
Usually given in tablet form, twice daily, or as a liquid formulation applied to skin on the inner ear, for cats that just won’t take a pill. Treatment is lifelong – ceasing medication quickly results in the hyperthyroidism returning again.
surgery: performed to remove the affected thyroid gland(s) and can
cure the disease. Surgery is performed usually after a period of anti-thyroid medication (minimum of four weeks). There are a few risks involved with this procedure and your vet will discuss these with you.
diet: a specialised diet is now available. When it’s the only food your cat is fed, thisdiet prevents the production of the thyroid hormone.
radioactive iodine treatment: involves an injection that exposes the abnormal tissue in the thyroid gland to radiation and can result in a cure for hyperthyroidism. This treatment involves quarantining the cat for at least 30 days. It’s currently only available in specialist centres in the eastern states but is expected to become available in Perth in 2016.
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