Our Vancouver vets are here to explain hyperthyroidism, a condition that commonly affects middle-aged and senior cats. We'll cover the symptoms, diagnosis, and treatment options for this disease.

What is hyperthyroidism in cats?

Hyperthyroidism is a common disorder in cats that occurs when their thyroid glands produce too much thyroid hormones.

These hormones regulate many body processes and metabolic rates, and excessive hormone production can cause severe clinical symptoms.

Cats with hyperthyroidism tend to lose weight despite increased appetite because they burn energy too quickly. We'll go over other symptoms below.

What are the symptoms of hyperthyroidism in cats?

Usually seen in cats who are middle-aged and older. Most are older than 10 - between 12 and 13 years old - when the disease becomes an issue. Female and male cats are equally impacted.

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.

In advanced cases, some cats may pant when they are stressed (an unusual behavior for kitties). While we note that most cats have a good appetite and are restless, some may feel weaker, lethargic, or have a lack of appetite. The key is to watch for significant changes in your cat and have them addressed earlier rather than later.

These symptoms are usually subtle and gradually become more severe as the underlying disease worsens. Other diseases can also complicate and mask these symptoms, so seeing your vet early is important.

What causes hyperthyroidism?

Most cats develop hyperthyroidism due to benign changes in their bodies that cause enlargement of both thyroid glands, known as nodular hyperplasia.

The cause of this change is similar to toxic nodular goitre in humans, although it is not entirely clear. In rare cases, a malignant tumor called thyroid adenocarcinoma can cause hyperthyroidism in cats.

What are the long-term complications of hyperthyroidism?

If left untreated, hyperthyroidism can cause heart problems such as an increased heart rate and changes in the heart's muscular wall, which can eventually lead to heart failure.

High blood pressure is another potential complication, which can cause damage to organs like the brain, kidneys, heart, and eyes. If your cat is diagnosed with hypertension along with hyperthyroidism, medication will be needed to control blood pressure.

Hyperthyroidism and kidney disease are often seen together in older cats, so both conditions must be closely monitored and managed as treating hyperthyroidism can sometimes negatively affect kidney function.

How is hyperthyroidism diagnosed?

Diagnosing hyperthyroidism in senior cats can be challenging. Your vet will perform a physical exam and feel your cat's neck for an enlarged thyroid gland. At Sharon Lakes Animal Hospital, our Charlotte vets have expertise in internal medicine and access to various diagnostic tools and treatments.

Since other common diseases in senior cats have similar symptoms to hyperthyroidism, a battery of tests will be required for an accurate diagnosis. These tests include a CBC, urinalysis, and chemistry panel to rule out diabetes and kidney failure.

Although a simple blood test that shows elevated T4 levels can provide a definitive diagnosis, this may not always be the case for all cats due to concurrent illnesses or mild cases of hyperthyroidism. In such cases, T4 levels may fluctuate, or elevated T4 levels may be due to another illness influencing the results.

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

Is hyperthyroidism in cats painful? 

Hyperthyroidism in cats is usually not painful, but it can cause discomfort due to symptoms such as weight loss, increased appetite, vomiting, diarrhea, and restlessness.

However, if left untreated, hyperthyroidism can lead to complications like heart disease, which can be painful for cats. Diagnosing and managing hyperthyroidism promptly to prevent complications is important, and consulting with a veterinarian is the best course of action if you are worried about your cat's health.

How will my vet treat my cat’s hyperthyroidism?

Your vet may choose one of several treatment options for your cat’s hyperthyroidism, based on your pet’s specific circumstances and the advantages and disadvantages of each option. They may include:

  • 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.

If your cat needs care, contact our veterinarians at Vancouver to book an appointment.