Feline hyperthyroidism is a condition that occurs when the thyroid gland produces too much of the hormone thyroxine (T4). Too much T4 can lead to symptoms such as weight loss, hyperactivity, and increased appetite. These symptoms may worsen if left untreated. Hyperthyroidism in cats can be diagnosed with a blood test. Treatment options include medication, dietary changes and radioactive iodine therapy. Fortunately, there are many treatments available for cats with hyperthyroidism. Here's what you need to know about this condition and its treatment options.

What is the thyroid gland and what does it do?

The thyroid gland is made up of two small glands located in the neck. The thyroid gland produces two hormones: thyroxine (T4) and triiodothyronine (T3). These hormones help to control the body's metabolism. Thyroid hormones aid in the control of heat production and carbohydrate, fat, and protein metabolism. Thyroid hormones also boost sympathetic nervous system activity, with varying effects on various organs.

What is hyperthyroidism in cats?

Hyperthyroidism is a condition in which the abnormal thyroid tissue and gland produce too much of the hormone thyroxine (T4). Hyperthyroidism can be defined as having high levels of T4, but there are other factors that play into hyperthyroidism. This includes an increased conversion of T3 to T4 and an increased sensitivity of the cells to the thyroid-stimulating hormone, TSH. All of these factors together can lead to an increase in thyroid hormone levels and the development of hyperthyroidism.

What are the signs of hyperthyroidism in cats?

The most common clinical signs of feline hyperthyroidism are weight loss, hyperactivity, increased appetite, increased thirst and urination. Other symptoms can include vomiting, a rapid heart rate (tachycardia), aggression, and increased vocalization, especially at nighttime. If left untreated, your cat's health may decline significantly. In addition, many cats with hyperthyroidism will have elevated blood pressure (hypertension). Weight loss with an increased appetite is a strong indicator that your cat may have hyperthyroidism, especially if your cat is greater than 12 years of age. Inflammatory bowel disease is another condition that can cause weight loss in cats with an increased appetite.

Diagnosis of hyperthyroidism in cats

Your veterinarian will typically use a blood test to diagnose feline hyperthyroidism. This is because there are no specific clinical signs that can be attributed to hyperthyroidism in cats, so they must rely on the results of your cat's blood tests. Since TSH levels vary greatly between cats with hyperthyroidism and normal cats, it may be difficult to diagnose hyperthyroidism based on TSH levels alone. Therefore, your veterinarian will likely on blood tests in order to confirm the diagnosis of hyperthyroidism. Typically, elevated T4 levels are diagnostic for hyperthyroidism in cats.

Treatment for hyperthyroidism in cats

There are a few different treatment options for hyperthyroidism in cats. The most common treatments include medication, dietary changes and radioactive iodine therapy.

Medication - Methimazole

Medication is the most common treatment for hyperthyroidism in cats. This typically involves taking oral medication every day to decrease your cat's thyroid hormone levels. There are a few different medications that can be used to treat hyperthyroidism in cats, but methimazole is the most common. This medication works by inhibiting the production of thyroid hormone. Typically, cats are dosed once to twice a day.

Dietary Changes

In some cases, dietary changes may also help to decrease your cat's thyroid hormone levels and manage hyperthyroidism. This typically involves feeding your cat a diet that is low in iodine, such as Hill's Prescription Diet y/d. Iodine is required for the synthesis of thyroid hormones, so if there is less iodine available, the thyroid gland will produce less thyroid hormone. It is extremely important that your cat does not consume any treats or other food while being fed the prescription diet. Even a little amount of other food can cause the thyroid gland to resume producing excessive levels of thyroid hormone.

Radioactive iodine treatment

In some severe cases, radioactive iodine therapy may be an option. This involves giving your cat a very small dose of radiation that will kill the cells in the thyroid gland that produce excessive levels of thyroid hormone. These dead cells are then absorbed into your cat's body and eventually removed through their gastrointestinal tract. Because this treatment requires specialized handling and procedures, it is only available at certain referral veterinary hospitals. This treatment is typically reserved for cats that are not responding well to other therapies or when hyperthyroidism has led to severe life-threatening complications like heart disease, kidney problems and high blood pressure (hypertension).

Frequently Asked Questions (FAQs)

Are certain cats more likely to develop hyperthyroidism?

Cats greater than 12 years of age are more likely to develop hyperthyroidism. However, cats as young as five can also be affected by the condition. Male and female cats appear to be equally at risk for developing this disease.

Will my cat be cured with treatment?

Unfortunately, hyperthyroidism is a condition that generally has no cure. However, many cats can be successfully treated for this disease with medications or other therapies which will reduce their thyroid hormone levels to normal and keep them stable over time. The only chance at a cure would be through radioactive iodine therapy, whereas most cats do not require any medications afterwards.

What are the side effects of treatment?

Some cats can show intense itchiness (pruritus) with methimazole treatment. In addition, some cats may have gastrointestinal side effects from methimazole treatment. In those cats, switching to a transdermal form of methimazole can be beneficial.

Furthermore, some cats that have underlying kidney disease should have extreme caution when starting treatment for hyperthyroidism. A reduction in thyroid hormone (i.e. treating hyperthyroidism) can cause reduced renal blood perfusion and exacerbate the underlying renal disease. Please discuss this with your veterinarian prior to treating hyperthyroidism in your cat.

What is the prognosis for hyperthyroidism?

The prognosis for hyperthyroidism is generally good, as most cats respond well to treatment. However, some cats may require lifelong therapy and regular monitoring. When all other therapies have failed or when there are significant side effects caused by methimazole therapy, radioactive iodine therapy may be the best option for your cat.

Can hyperthyroidism in cats be prevented?

Unfortunately, there is currently no way to prevent hyperthyroidism in cats.

What Breeds Are Prone to Hyperthyroidism?

While hyperthyroidism can affect any breed of cat, some breeds appear to be at increased risk for developing the disease. These include:

- Siamese
- Abyssinian
- Burmese

What are the methimazole side effects in cats?

Potential side effects of methimazole are vomiting and intense itchiness (pruritus). If you notice that your cat is vomiting on methimazole, using a transdermal form would be beneficial. If you notice that your cat is excessively itchy after starting methimazole, you should consider using a prescription diet designed to treat hyperthyroidism or radioactive iodine therapy.

Hyperthyroidism in cats is a condition that occurs when the thyroid gland produces too much of the hormone thyroxine (T4). Too much T4 can lead to symptoms such as weight loss, hyperactivity, and increased appetite. These symptoms may worsen if left untreated. Hyperthyroidism can be diagnosed with a blood test. Treatment options include medication, dietary changes and radioactive iodine therapy. Fortunately, there are many treatments available for cats with hyperthyroidism depending on what your cat needs. Let's talk about some of these treatment methods so you know how to care for your feline friend!