What is Hyperthyroidism in Cats?

Introduction

When Oliver, a charming Ragdoll cat, started showing signs of weight loss and increased appetite, his owner, Grace, knew something was off. Worried about these unexpected changes, she took Oliver to their trusted veterinarian for a thorough check-up. After conducting blood tests, the veterinarian diagnosed Oliver with hyperthyroidism, a common hormonal disorder in cats.

Hyperthyroidism in cats is an endocrine disorder with too much thyroid hormone circulating in the blood. This excess thyroid hormone leads to symptoms such as weight loss, heart palpitations, anxiety, and nervousness. In addition, in some cases, cats with Hyperthyroidism may experience swelling in the neck area due to enlargement of the thyroid gland.

There are four types of Hyperthyroidism: toxic nodular goiter (TN), diffuse goiter (DG), Graves’ disease, and carcinoma (CA).

• Toxic nodular goiters are tumors that grow in the thyroid gland. These tumors can be benign or malignant. Benign toxic nodules usually appear as large lumps under the skin, while malignant ones tend to spread into surrounding tissues. Malignant toxic nodules are rare in cats, but benign ones are common. Toxic nodules are typically found during routine physical exams.
• Diffuse goiters are thyroid nodules that appear diffusely over the entire gland. They are usually benign tumors that grow slowly over time. Diffuse goiters are typically found in older animals, especially female dogs and cats.

While diffuse goiters aren’t dangerous, they can affect your pet’s health. Some pets develop symptoms related to Hyperthyroidism, including weight loss, increased appetite, excessive energy, and urination problems. However, these signs can be mistaken for other conditions, so it’s important to rule out other causes of weight loss before diagnosing Hyperthyroidism.

• Graves’ disease is a condition that causes hyperactivity in the thyroid gland. Hyperthyroidism occurs when the thyroid produces too much hormone, causing symptoms like weight loss, increased appetite, heart palpitations, and anxiety.

There are two types of Graves’ disease: exogenous and endogenous. Exogenous refers to autoantibodies against thyroglobulin, while endogenous relates to antibodies against TSH receptors. Both forms of the disease require treatment with anti-thyroid drugs.

• Carcinomas begin in cells, part of our body’s immune system. Carcinomas are classified based on the type of cell they originate from. Some cancerous tumors develop from epithelial tissue, while others arise from connective tissues.

Epithelial tissue includes skin, mucus membranes, glands, and other organs that line cavities within the body. Connective tissue includes tendons, ligaments, bones, cartilage, blood vessels, nerves, and muscles.

Where are Your Cat’s Thyroid Glands?

Cats have a single thyroid gland that is located near the windpipe. This gland produces three main types of hormones: thyroxine (T4), triiodothyronine (T3), and reverse triiodothyronine(rT3). These hormones regulate metabolism, growth, reproduction, and nervous system function. In addition, cats produce some of their iodine from dietary sources, which helps maintain healthy levels of thyroid hormone production.

What Do Your Cat’s Thyroid Glands Do?

The thyroid gland regulates body temperature, heart rate, and cardiac output and controls how much energy is stored in fat cells.

Your cat’s thyroid gland produces several important hormones essential for normal body functions. For example, thyroid hormones help control how fast your cat burns calories, regulate blood sugar levels, maintain healthy bones, muscles, hair, nails, teeth, and skin, and help maintain proper brain development.

When you feed your cat properly, it will make enough thyroid hormone to meet its needs. However, if your cat doesn’t eat enough, it won’t make enough thyroid hormone to meet its daily requirements. As a result, your cat will begin losing weight.

Cats who overeat often become overweight. They’re prone to developing obesity because their bodies don’t use stored fat efficiently. As a result, their thyroid glands enlarge and overproduce thyroid hormone. Enlarged thyroid glands cause your cat to retain water, leading to increased weight.

Causes of Feline Hyperthyroidism

In most cases, it is caused by an overactive thyroid gland. However, sometimes the thyroid gland produces too little thyroid hormone driving a condition known as hypothyroidism.

Cat’s hyperthyroidism usually develops due to an autoimmune disorder called feline hyperadrenocorticism (HAC). HAC is caused by the body attacking itself, resulting in inflammation and damage to the adrenal glands.

Cats with Hyperthyroidism may also develop diabetes mellitus. Diabetes affects the ability of blood vessels to transport glucose into cells and use it for energy.

As a result, the pancreas secretes large amounts of insulin to help regulate blood sugar levels. When the thyroid gland becomes hyperactive, it increases the number of thyroid hormones produced. Insulin does not work well in the presence of high levels of thyroid hormones because the thyroid gland uses most of the insulin produced by the pancreas.

As a result, blood sugar levels rise and become unstable. In addition, the liver cannot process fats properly, leading to fatty deposits around the kidneys.

What Are Breeds Prone to Hyperthyroidism?

Hyperthyroidism is most common in older cats, especially those over ten. It occurs less frequently in younger cats. Several breeds of cats are prone to Hyperthyroidism, including the Maine Coon, Persian, Ragdoll, Siamese, Sphynx, and Turkish Angora. These breeds tended to be larger than others and predisposed toward obesity.

It’s also important to remember that certain breeds are more likely to develop Hyperthyroidism, but it can happen to any breed. So as long as your pet eats healthy food and exercises regularly, they shouldn’t have any problems.

What are the Symptoms of Hyperthyroidism in Cats?

Symptoms of Hyperthyroidism in cats usually appear as weight loss despite increased appetite, excessive urination, aggression, depression, restlessness, and difficulty breathing. These are just some of the possible symptoms.

Other signs of Hyperthyroidism include vomiting, diarrhea, muscle wasting, lethargy, lack of coordination, seizures, heart problems, kidney failure, high blood pressure, and enlarged glands. If left untreated, Hyperthyroidism can lead to death.

Diagnosis for Cats with Hyperthyroidism

To diagnose Hyperthyroidism, veterinarians perform a physical examination, blood tests, thyroid ultrasound scans, and Nuclear Medicine scans. In addition, your vet will check for evidence of organ dysfunction, such as an irregular heartbeat, poor muscle tone, rapid breathing, and changes in behavior.

• Blood test

Thyroid-stimulating hormone (TSH), free thyroxine (fT4), and total triiodothyronine (tT3). TSH checks how well the pituitary gland is producing thyroid hormones. fT4 measures what level of thyroid hormones are circulating in the bloodstream. tT3 checks for abnormalities in thyroid function.

• Nuclear Medicine Scan

Technetium-99m pertechnetate is injected into the vein. After about 30 minutes, images are taken to see if the thyroid gland is usually working.

• Ultrasound

An ultrasound uses sound waves to produce pictures of internal organs. A small amount of contrast material is given intravenously to highlight areas inside the body.

Treatments Options for Hyperthyroidism

Treatment option includes medication, radioiodine therapy, and surgery. These treatments depend on the type of hyperthyroid syndrome present. 

• Medications are typically prescribed for your cat’s entire life. They work by blocking the production of thyroid hormones. For example, your vet might prescribe one of the following medications: propylthiouracil, methimazole, carbimazole, or iodine 131. These drugs must be administered daily for the rest of your pet’s life.
• Radioiodine therapy is an effective way to manage Hyperthyroidism in some cats. Approximately 95% of all hyperthyroid cases are curative within three months of radioiodine therapy. It involves injecting patients with radioactive iodine. The radioactive iodine attaches itself to the thyroglobulin protein found inside the thyroid cells.

Thyroglobulin is a large protein that holds onto iodine. When the radioactive iodine attaches to the thyroglobulin, it becomes radioactive and destroys the thyroid cells. This causes the thyroid gland to shrink and stop producing excess thyroid hormones. A second injection of radioiodine is given about six months later.

• Surgery is another viable option if medication isn’t working. In this case, your veterinarian will cut out the affected thyroid gland. Surgical thyroid gland removal is typically recommended for cats with toxic nodular or diffuse goiter. However, surgery carries risks such as bleeding, infection, and scarring.

Cats That Have Been Diagnosed With Hyperthyroid Disease Should Receive Regular Monitoring after Treatment

After treating Hyperthyroidism in cats, veterinarians recommend monthly blood tests to monitor thyroid function and how well their bodies respond to the medication. These tests measure levels of T4 and T3 hormones in the bloodstream.

It’s recommended that owners continue to monitor their pet’s health after treatment. Monitoring includes checking for signs of lethargy, weight loss, vomiting, diarrhea, increased appetite, and other hypothyroidism-related symptoms.

Frequently Asked Questions