For middle-aged and senior cats, hyperthyroidism can be a problem. Our White Settlement veterinarians explain the disease, symptoms, diagnosis, and treatment options in this post.

What is hyperthyroidism in cats?

Hyperthyroidism happens when a cat’s thyroid glands are overactive. It’s a very common disorder caused by an increase in the production of thyroid hormones by the thyroid glands, which are located in the neck.

Thyroid hormones are used to control the metabolic rate and regulate many processes in the body, and when too much of the hormone is produced, clinical symptoms can be quite dramatic, making cats very sick.

Cats suffering from hyperthyroidism tend to burn energy too quickly, which results in weight loss despite eating more food and experiencing an increase in appetite. We’ll discuss more symptoms below.

What are the symptoms of hyperthyroidism in cats?

Cats that are older or in the middle of their lives are more likely to have hyperthyroidism. When the disease becomes a problem, most children are older than 10 years old, between the ages of 12 and 13. Both male and female cats are affected.

Hallmark signs of hyperthyroidism include:

  • Increase in thirst
  • Increased irritability or restlessness
  • Increase in heart rate
  • Poor grooming habits
  • Typically a healthy or increased appetite

Some cats will also have mild to moderate diarrhea and/or vomiting, while others will seek cooler places to lounge and have a low tolerance for heat.

When cats are stressed, they may pant in advanced cases (an unusual behavior for kitties). While most cats are active and have a good appetite, some may be weaker, lethargic, or have a lack of appetite. The key is to keep an eye out for significant changes in your cat and address them as soon as possible.

These symptoms are usually subtle to start and gradually become more severe as the underlying disease gets worse. Other diseases can also complicate and mask these symptoms, so it’s important to see your vet early.

What causes hyperthyroidism?

For most kitties, benign (non-cancerous) changes in their bodies can trigger the condition. Both thyroid glands are most often involved and become enlarged (the clinical change is nodular hyperplasia, and it resembles a benign tumor).

We don't know what causes the change, but it's similar to hyperthyroidism in humans (clinically named toxic nodular goiter). Thyroid adenocarcinoma, a cancerous (malignant) tumor, is the underlying cause of this disease in a small percentage of cases.

What are the long-term complications of hyperthyroidism?

Left untreated, hyperthyroidism can impact the function of the heart, changing the organ’s muscular wall and increasing heart rate. It can eventually lead to heart failure.

High blood pressure is another possible complication (hypertension). Though it is less common, it can cause damage to a variety of organs, including the brain, kidneys, heart, and even the eyes. If your cat has hypertension in addition to hyperthyroidism, medication to control blood pressure will be required.

Hyperthyroidism and kidney disease often occur at the same time, as they are both commonly seen in older cats. When both these conditions are present, they need to be closely monitored and managed as managing hyperthyroidism may sometimes adversely affect kidney function.

How is hyperthyroidism diagnosed?

Diagnosis of hyperthyroidism in senior cats can be tricky. Your vet will complete a physical exam and palpate your cat’s neck area to look for an enlarged thyroid gland.

A battery of tests will likely be needed to diagnose hyperthyroidism in your cat, as many other common diseases experienced by senior cats (intestinal cancer, chronic kidney failure, diabetes, inflammatory bowel disease, and more) share clinical symptoms with hyperthyroidism.

A complete blood count (CBC) urinalysis and chemistry panel can help rule out kidney failure and diabetes.

A simple blood test showing elevated T4 levels in the bloodstream may be sufficient for a definitive diagnosis, though this is not true for all cats due to concurrent illnesses or mild cases of hyperthyroidism, which can cause fluctuating T4 levels or show elevated T4 levels if another illness is interfering with the result.

If possible, your vet may also check your cat’s blood pressure and perform an electrocardiogram, chest x-ray, or ultrasound.

How will my vet treat my cat’s hyperthyroidism?

Based on your cat's unique circumstances and the benefits and drawbacks of each treatment option, your veterinarian may recommend one of several treatment options for hyperthyroidism. They may include the following:

  • Radioactive iodine therapy (likely the safest and most effective treatment option)
  • Antithyroid medication, administered orally, to control the disease for either the short-term or long-term
  • Surgery to remove the thyroid gland
  • Dietary therapy

What is the prognosis for cats with hyperthyroidism?

Your kitty’s prognosis for hyperthyroidism will generally be good with appropriate therapy, administered early. In some cases, complications with other organs can worsen the prognosis.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Do you believe your cat may be suffering from Hyperthyroidism? Contact Frontier Veterinary Hospital today. We can assess your cat and make recommendations on the next steps.