Skip to Main Content
Ask About Financing

Hyperthyroidism in Cats

Middle-aged and senior cats are often diagnosed with hyperthyroidism, along with other conditions. In this post, our Bonita Springs vets discuss the causes, signs, and treatment of hyperthyroidism in cats.

Feline Hyperthyroidism

Hyperthyroidism is a very common disorder that occurs when the thyroid glands (which are located in the neck) produce too many thyroid hormones.

These hormones are used to control the body’s metabolic rate and regulate many processes. Excessive production of thyroid hormones can cause dramatic clinical symptoms that can result in severe illness.

Cats who suffer from hyperthyroidism tend to burn energy too quickly, leading to weight loss even as they experience an increase in appetite and eat more food.

Signs of Hyperthyroidism in Cats

The condition is usually seen in middle-aged and senior cats (with most older than 10 years - between 12 and 13 years old on average - when the disease develops). Male and female cats are equally impacted.

Signs of hyperthyroidism include:

  • Poor grooming habits
  • Increase in thirst
  • Increase in heart rate
  • Increased appetite
  • Increased restlessness or irritability

Mild to moderate vomiting and/or diarrhea can also be an issue for some cats with hyperthyroidism, while others will have a low tolerance for heat and therefore look for cooler places to lounge.

In severe or advanced cases, you may notice your furry feline pant when he or she is stressed (an unusual behavior for cats). While most cats may act restless and have a healthy appetite, some may feel lethargic, weak, or exhibit a lack of appetite. The rule of thumb to follow is that any significant changes should be examined and addressed by your vet.

These symptoms are usually subtle when they first develop and gradually become more severe as the underlying disease worsens. Other diseases may also complicate and mask these symptoms, so it’s critical to see your vet for early detection and diagnosis.

Causes of Hyperthyroidism in Cats

For most cats, hyperthyroidism is caused by benign (non-cancerous changes in their bodies). Both thyroid glands are typically involved and become enlarged (the clinical name for this is nodular hyperplasia, which resembles a benign tumor).

Though it’s not exactly clear what causes the change, hyperthyroidism in cats is similar to the same condition in humans (clinically referred to as toxic nodular goiter). In rare cases, thyroid adenocarcinoma, a cancerous or malignant tumor, is the underlying cause of the disease.

Possible Long-Term Complications

Left untreated, hyperthyroidism can change the heart’s muscular wall, which results in increased heart rate and alters how the heart functions. It can also eventually lead to heart failure.

High blood pressure (hypertension) is another potential complication, though it is seen less often. This can result in several organs - including the heart, eyes, kidneys, and brain - being damaged. If your cat is diagnosed with hypertension along with hyperthyroidism, he or she will need medication to control blood pressure.

Hyperthyroidism and kidney disease are often co-occurring conditions, as older cats are commonly diagnosed with them. When this is the case, they need to be closely monitored and managed, as the methods used to manage hyperthyroidism can impact kidney function.

Diagnosing Hyperthyroidism in Cats

Your vet will perform a physical exam and palpate your cat’s neck area to see if the thyroid gland is enlarged. A battery of tests will likely be required to make a definitive diagnosis, as senior cats can experience many other common diseases (such as chronic kidney failure, inflammatory bowel disease, intestinal cancer, diabetes, and more) that share clinical symptoms with hyperthyroidism.

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

While a simple blood test showing elevated T4 levels in the bloodstream may be sufficient for a clinical diagnosis, this is not true for 100% of cats due to mild cases of hyperthyroidism or concurrent illnesses. These can result in fluctuating T4 levels or, if another illness is impacting the result, showing elevated T4 levels.

Your vet may also check your cat’s blood pressure and complete an electrocardiogram, ultrasound, or chest X-ray.

Treating Hyperthyroidism in Cats

One of several treatment options may be chosen for your cat’s specific case of hyperthyroidism, based on your pet’s individual circumstances and the advantages and disadvantages of each option. Treatment options can include:

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

Life Expectancy of Cats With Hyperthyroidism

The prognosis for feline hyperthyroidism is generally good with appropriate therapy and treatment, administered early. In some cases, the condition can lead to complications with other organs, which can worsen the prognosis.

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

Concerned that your cat is showing signs of hyperthyroidism? Contact our Bonita Springs vets today.

Our 24/7 Emergency Care in Bonita Springs 

Contact (239) 992-8387