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    896 N. Burlington Boulevard, Burlington, WA 98233 US


  • The Chuckanut Valley Feline Center

    1214 Dupont Street, Bellingham, WA 98225 US


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Hyperthyroidism in Cats

Hyperthyroidism in Cats

Hyperthyroidism is a condition sometimes seen in middle-aged and senior cats. Today, our Burlington and Bellingham vets talk about hyperthyroidism in cats, including its symptoms, causes, and the treatments available.

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 regulate many processes in the body and to control the metabolic rate, and when too much of the hormone is produced, clinical symptoms can be quite dramatic and make cats severely 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.

Signs & Symptoms of Hyperthyroidism in Cats

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

Here are some common signs of hyperthyroidism in cats:

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

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 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 as early as possible.

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

The Causes of Cat Hyperthyroidism

Benign (non-cancerous) changes in a cat's body can trigger the condition. Most of the time, both thyroid glands are involved and become enlarged (the clinical change is nodular hyperplasia, and it resembles a benign tumor).

While we aren't sure what causes this change, it's similar to hyperthyroidism in humans (clinically named toxic nodular goiter). Rarely, a cancerous (malignant) tumor called thyroid adenocarcinoma is the underlying cause of this disease.

The Long-Term Complications of Hyperthyroidism in Cats

If hyperthyroidism goes untreated it can impact the function of your cat's heart, changing the organ’s muscular wall and increasing heart rate. It could eventually result in heart failure.

High blood pressure (hypertension) is another potential complication. While this isn't seen as often, it can cause damage to several organs including the brain, kidneys, heart, and even the eyes. If your vet diagnoses your cat with hypertension in addition to hyperthyroidism, medication will be required to control blood pressure.

Hyperthyroidism and kidney disease often happen at the same time, as they are both fairly common 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.

Diagnosing Cats With Hyperthyroidism

Diagnosing 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. At Chuckanut Valley Vet Clinic and Chuckanut Feline Center, our Burlington and Bellingham vets are trained in internal medicine and have access to a variety of diagnostic tools and treatment methods.

A range of tests will likely be required to diagnose your cat's hyperthyroidism, as many other common diseases seen in 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 enough for a definitive diagnosis, however, this is not true for 100% of cats because of concurrent illnesses or mild cases of hyperthyroidism, which can result in fluctuating levels of T4 or showing elevated T4 levels if another illness is influencing the result.

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

Treating Hyperthyroidism In Cats

Your vet might select one of several treatment options for your cat’s hyperthyroidism, depending on your furry friend’s specific circumstances and the advantages and disadvantages of each option. Your kitty's treatment may include:

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

The Prognosis For Cats That Have Hyperthyroidism

The prognosis for cats with hyperthyroidism is generally good if the appropriate therapy is administered early. Sometimes, complications with other organs can make the prognosis worse.

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 you think your cat may have hyperthyroidism, contact our Burlington and Bellingham vets today and schedule an appointment.

New Patients Welcome

Chuckanut Valley Vet Clinic and Chuckanut Feline Center is accepting new patients! Our experienced vets are passionate about the health of Burlington and Bellingham companion animals. Get in touch today to book your pet's first appointment.

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