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

What is hyperthyroidism in cats?

When a cat's thyroid glands are overactive, this is known as hyperthyroidism. Thyroiditis is a very common condition caused by an increase in thyroid hormone production by the thyroid glands 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 with hyperthyroidism burn their energy too quickly, resulting in weight loss despite eating more food and having an increased appetite. More symptoms will be discussed further down.

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.

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 mild at first, but as the underlying disease worsens, they become more severe. Other diseases can exacerbate and mask these symptoms, so it's critical to see your veterinarian as soon as possible.

What causes hyperthyroidism in cats?

Most cats develop the condition as a result of benign (non-cancerous) changes in their bodies. Most of the time, both thyroid glands are affected and enlarge (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.

Because hyperthyroidism and kidney disease are both common in older cats, they frequently occur together. When both of these conditions are present, they must be closely monitored and managed, as hyperthyroidism treatment can hurt 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. 

Many other common diseases in senior cats (intestinal cancer, chronic kidney failure, diabetes, inflammatory bowel disease, and more) share clinical symptoms with hyperthyroidism, so a battery of tests will likely be required to diagnose hyperthyroidism in your cat.

Kidney failure and diabetes can be ruled out with a complete blood count (CBC), urinalysis, and chemistry panel.

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 do you treat hyperthyroidism in cats?

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.

Is your cat experiencing symptoms of hyperthyroidism? Contact our Rochester vets today for an evaluation.