Hyperthyroidism is a term used to describe an overactive thyroid gland. There are two Thyroid glands located within the neck. The exact mechanism is unclear, but these glands become enlarged and start to release excessive thyroid hormone. Thyroid hormones play lots of important roles in the body but their regulation of metabolism is most significant. 

Hyperthyroidism is a very common condition in older cats. The typical presentation includes a cat which is eating excessively but losing weight. Other common signs include vomiting, diarrhoea and excessive drinking. Cats can also have a hyperactive demeanour, increased restlessness, an unkempt hair coat and increased vocalisation.

Without treatment cats will continue to be excessively hungry, thirsty and lose weight. This isn’t necessarily painful for them but it can impact on their quality and length of life. Thyroid hormones can also stimulate the heart muscle; with prolonged exposure this can lead to significant heart disease which can have more serious consequences.

So How Can We Manage Hyperthyroidism?

Radio-iodine treatment

The gold standard treatment for hyperthyroidism is radio-Iodine therapy; it has high rates of success and can significantly increase survival time. It involves an injection of radioactive Iodine which targets the affected thyroid cells. It is important to ensure that this therapy is appropriate for your cat and that any other illnesses are stable and well controlled. Specialist centre’s have to perform this therapy and your cat will require at least a 2 week stay in most of these facilities. Once at home there will be a period of time where their urine and faeces is still radioactive and must be handled safely. We have had a few of our own patients visit the Hyperthyroid cat centre with really good results. Due to it’s specialist nature this treatment can be expensive and may not be an option for those cats that are not insured.

Oral medications

In many cats we start long term oral medications. These work by reducing the production of thyroid hormones. Medications come in both tablet and liquid formulations and are generally given twice daily. Initial stabilisation and control of the thyroid level can take a couple of weeks and requires repeated blood tests during this time. Once we have found the effective dose you should see an improvement in your pet’s clinical signs. For example, their appetite and thirst should normalise and they should put on weight. Long term monitoring of your cat’s thyroid level is continued, this is based on how they are doing at home but the general recommendation is every 3-6 months. Of course, administration is a big factor to take into account when selecting this option.

Surgery

It is possible to surgically remove the affected thyroid gland. Firstly, we have to make the decision whether a general anaesthetic and surgical procedure is appropriate for the patient. Some cats will present unwell and many will have concurrent kidney and heart disease therefore surgery is often not the treatment of choice. Some cats will also have ectopic thyroid tissue; this is an abnormal piece of thyroid tissue located elsewhere in the body, its presence means that surgical removal of the normally located glands may not completely resolve your pets clinical signs. Your cat will also require stabilisation on oral medications before embarking on the surgery. In the surgery, the affected gland is removed. However, it is common for the remaining gland to later develop the same condition and so multiple surgeries can be required. Post surgery, there can be the risk of low calcium levels; the parathyroid gland which regulates calcium is closely situated to the thyroid gland so can be disrupted during the surgery. As you can see, there can be lots of things to consider and on a whole surgery is not something we generally recommend for our patients.

Diet

Iodine is required to produce thyroid hormones. Therefore, restricted Iodine diets have been formulated to help manage this condition.  Only this diet must be fed for this to be effective. Limitations arise with fussy cats that won’t consistently eat the diet and this approach is not really suitable for outdoor cats that can hunt and eat elsewhere.