Hyperthyroidism in Cats

A tip from Garret Turley of Pet Doctors

It is caused by the development of a (usually) benign growth in one or both of the cats thyroid glands. The thyroid glands control the metabolic rate and when they develop an adenoma (benign cancer) they produce too much thyroid hormone (hence hyper-, -thyroidism). No-one knows as yet what causes this disease but it didn’t exist in the UK until about 20 years ago. It was first identified in the USA some 10 years beforehand and initially it was a disease limited entirely to elderly cats. However, today we check cats of all ages who display some of the symptoms.

There is a range of symptoms associated with hyperthyroidism and an individual cat may display any or all of them. They include increased drinking & urinating, increased appetite (common) with weight loss, hyperactivity, diarrhoea, the presence of an enlarged thyroid gland (this can be hard to detect on occasion), a markedly raised heart rate and an ‘anxious’ expression. If left untreated hyperthyroidism will cause death. The elevated heart rate is a symptom of the damage (increased thickening and stiffening) to the heart muscle that is called hypertrophic cardiomyopathy.

The good news is that once diagnosed the disease can be treated effectively reversing much of the damage caused by the disease. Diagnosis is based upon clinical signs and must be confirmed with a blood test. Treatment is initially by tablets to stabilise the condition especially the heart damage. After about 1 month a further blood test is taken to confirm that the medication is working. Cat owners may consider using medication long-term with regular monitoring by blood tests or the option of surgery to remove one or both of the thyroid glands may be taken. Each case is of course an individual and anyone who has a cat with hyperthyroidism should discuss thoroughly the available options with their veterinary surgeon.