Hyperthyroidism, or an overreactive thyroid, is extremely common as cats get older. Find out what causes the condition and how to treat it.
What is hyperthyroidism?
Hyperthyroidism, otherwise known as an overactive thyroid, is where the thyroid glands in the neck develop abnormal tissues which increase the production of thyroid hormones. These hormones are responsible for regulating many processes in the body, including your cat’s metabolism, and when too much is produced, your cat can become seriously ill.
Hyperthyroidism is incredibly common as cats get older, with the average age of cats developing the condition between 12 and 13 years. If left untreated, the issue can cause serious problems for the heart and kidneys.
Causes of hyperthyroidism
In most cases, hyperthyroidism is caused by a non-cancerous tumour called an adenoma. While the underlying cause of this growth is still unknown, it could be a result of the cat’s diet or their environment.
In very rare cases (less than one to two per cent), a cancerous tumour can be the underlying cause of the condition.
Symptoms of hyperthyroidism are usually subtle to begin with, becoming more severe as the condition worsens.
These symptoms include:
• weight loss
• increased appetite and/or thirst
• increase activity, restlessness or irritability
• increased heart rate
• poor condition of fur or skin.
Some cats may also experience moderate diarrhoea and vomiting, and some may be noticeably intolerant of heat. In advanced cases of hyperthyroidism, your cat may even pant when they’re stressed.
Effects of hyperthyroidism
If left untreated, hyperthyroidism can cause an increased heart rate and changes to the wall of the heart; this can subsequently cause heart failure.
Although less common, an overactive thyroid can also cause high blood pressure which can cause damage to the eyes, kidneys, heart and brain.
While kidney disease is not a direct result of hyperthyroidism, it’s common as cats get older, so the two conditions are often present at the same time. If so, extra care is needed as an overactive thyroid can affect kidney function.
Thankfully, hyperthyroidism can be treated successfully through various methods to suit the individual case: medication, radioactive iodine therapy, surgery or diet.
A daily dose of anti-thyroid medication (available as tablets or liquid) blocks the excessive production of the thyroid hormone, therefore keeping the condition under control. It’s important to remember that these medications don’t cure the condition and they need to be taken for the rest of your cat’s life, along with regular monitoring tests with a vet. However, many cats live long and happy lives on this treatment.
Removing the affected tissues in an operation called a thyroidectomy is a common long-term or permanent solution. All animals have two thyroid glands, and either one or both can be removed depending on their condition. After the surgery, your vet may recommend regular blood tests to check the hormone levels are normal. Hypothyroidism, or an underactive thyroid, can sometimes develop from this surgery and while side effects are rare, your cat may experience loss of appetite, vomiting and tiredness.
Radioactive iodine therapy
Radioactive iodine therapy involves a simple injection under the skin which is absorbed by the abnormal thyroid tissue. The radioactive iodine destroys the affected tissues without harming the surrounding glands or tissues. This safe and effective treatment has a high success rate but is only available at specialist centres (including Medivet Enfield) can be expensive, and requires hospitalisation for three to six weeks.
Adopting a special diet with controlled iodine levels (which the thyroid needs to make hormones) can help manage hyperthyroidism. It’s imperative that cats on this form of treatment stick to the diet exclusively to ensure its success – this can be difficult if your cat goes out.
Can cats have underactive thyroids?
While an underactive thyroid, or hypothyroidism, is common in dogs, the condition is incredibly rare in cats. When hypothyroidism is seen in cats, it’s usually as a result of surgery to treat an overactive thyroid.
Numerous feline patients treated at Medivet 24 Hour Enfield have been given a new lease of life since special treatment was introduced two years ago.