Feline Hyperthyroid Disease

Hyperthyroidism occurs when the body produces an excess of thyroid hormones. Thyroid hormones are involved in a number of metabolic pathways, and excessive amounts lead to an overactive metabolism. Most cases of hyperthyroidism in cats are due to a benign enlargement of one or both of the thyroid glands, however a small percentage of cases are due to a malignant thyroid tumour.

What are the signs of hyperthyroidism?

As the thyroid hormones are involved in a number of body systems, it leads to a variety of clinical signs and multiple associated conditions. Hyperthyroid cats most commonly present with weight loss despite a large appetite, however they may have any of the following clinical signs:

excessive/increased thirst
increased urination
increased vocalisation
increased activity/restlessness
increased breathing rate
elevated heart rate
vomiting
diarrhoea
unkempt coat
inappetence
lethargy
enlarged thyroid gland

How do we diagnose hyperthyroidism?

The first step towards diagnosis begins with a thorough history and physical examination. Ultimately the diagnosis of hyperthyroidism is made using a blood sample, which measures the amount of thyroid hormones in the blood. The amount of thyroid hormones in the blood increases with the severity of the disease, and so in most cases the condition is easily identified. However, there are circumstances where the diagnosis may not be so straightforward; usually in the early stages of the disease, or if the patient is suffering with other illnesses. There are other tests available if this situation arises.

What is the treatment?

Fortunately hyperthyroidism is a treatable condition, as if left un-treated it will become life-threatening. There are many different treatment options available for feline hyperthyroidism, and the most appropriate one will depend on the individual patient:

Medical: This is the most widely used treatment option and comes in the form of tablets or transdermal gel. It can be used in the short-term to stabilise a hyperthyroid patient before undergoing a different treatment, or used long-term to manage the condition indefinitely. Patients will need regular check ups and blood tests to ensure accurate dosing Although rare, as with all medication, some individuals may experience side effects of the drug.

Surgical: This is ideally performed once a patient has been stabilised with medical treatment, as uncontrolled hyperthyroidism increases the risk of general anaesthesia. The surgery removes either one or both of the thyroid glands, and can result in complete cure of the condition. This is beneficial in cats where giving medication is particularly difficult. The risks associated with surgery are general anaesthesia and removal of the parathyroid glands which are involved with calcium regulation.

Radioiodine: This is considered the treatment of choice for cats with hyperthyroidism. It’s benefits are a single treatment that can cure the condition with minimal side effects. It is most effective and successful in patients who are otherwise healthy. The main risk associated with radioiodine treatment is causing irreversible hypothyroidism, that then requires ongoing thyroid supplementation. However, it is an extremely successful treatment option in the majority of cases.

Diet: There is a prescription diet available, which when fed exclusively, is a successful treatment option for hyperthyroidism. There is a wet and dry version available. This diet is perfect for patients that are difficult to give medication or are not suitable candidates for general anaesthesia or radioiodine treatment. The diet must be fed exclusively, which may make this treatment difficult in multicast households, or if the cat requires a prescription diet for another condition.