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Hyperthyroidism in Cats: Symptoms, Diagnosis & Treatments

Hyperthyroidism in Cats: Symptoms, Diagnosis & Treatments

As cats reach middle age and beyond, they may develop hyperthyroidism. This article from our Lisle veterinary explains what the condition is, the signs to look out for, how it's diagnosed, and the treatment options available.

What is hyperthyroidism in cats?

Hyperthyroidism is a common disorder in cats when their thyroid glands in the neck become overactive and produce an excess of thyroid hormone.

Thyroid hormones play a crucial role in controlling the body's metabolic rate and regulating various processes. When these hormones are produced excessively, cats may exhibit clinical symptoms that can make them very sick.

If your cat has hyperthyroidism, she may have a high energy burn rate, leading to weight loss despite consuming more food and having an increased appetite. Additional symptoms are described below.

What are the symptoms of hyperthyroidism in cats?

The symptoms typically manifest in middle-aged and senior cats, particularly those older than 10, usually between 12 and 13 years old. Both male and female felines are equally affected by the disease.

Trademark signs of hyperthyroidism include:

  • Increase in heart rate
  • Increase in thirst
  • Restlessness or irritability
  • Usually a healthy or increased appetite
  • Poor grooming habits

Some cats may experience mild to moderate vomiting and/or diarrhea, seek cooler places to rest, and have a low heat tolerance.

In advanced cases, some cats may pant when stressed, which is unusual behavior for cats. While most cats remain restless with a good appetite, some may experience a lack of appetite, lethargy, or weakness. It is crucial to monitor significant changes in your cat and seek veterinary attention sooner rather than later.

These symptoms initially appear subtly and can worsen gradually as the underlying disease progresses. Additionally, other diseases can complicate and mask these symptoms, underscoring the importance of early veterinary evaluation.

What causes hyperthyroidism?

Many cats experience the condition due to benign changes in their bodies, which often involve both thyroid glands becoming enlarged. This is referred to as nodular hyperplasia, resembling a benign tumor. The cause for this change is unclear, but it is similar to hyperthyroidism in humans, known clinically as toxic nodular goitre. In rare cases, the underlying cause may be a malignant cancerous tumor, such as thyroid adenocarcinoma.

What are the long-term complications of hyperthyroidism?

If hyperthyroidism is not treated, it can negatively impact the heart's function, causing changes in its muscular wall and increasing the heart rate. This may eventually lead to heart failure. Another possible complication is high blood pressure, also known as hypertension. Although not very common, it can damage several organs, including the heart, eyes, kidneys, and brain.

If your cat is diagnosed with hypertension and hyperthyroidism, medication will be necessary to control blood pressure. Additionally, older cats often experience both kidney disease and hyperthyroidism together. In such cases, close monitoring and management are necessary because managing hyperthyroidism can sometimes have an adverse effect on kidney function.

How is hyperthyroidism diagnosed?

Hyperthyroidism can be difficult to diagnose in senior cats. At Green Trails Animal Clinic, we take a comprehensive approach to internal medicine. Our vets have extensive experience in diagnosing and treating challenging cases.

To determine if your cat has hyperthyroidism, your veterinarian will perform a physical examination and examine the neck area for any signs of an enlarged thyroid gland. Since other common diseases in senior cats such as diabetes, cancer, chronic kidney failure, and inflammatory bowel disease can share clinical symptoms with hyperthyroidism, the veterinarian will likely conduct a battery of tests.

A chemistry panel and complete blood count (CBC) can rule out diabetes and kidney failure as potential causes. A definitive diagnosis may be achieved through a simple blood test that shows elevated T4 levels in the bloodstream. However, this may not be conclusive for all cats due to concurrent illnesses or mild cases of hyperthyroidism that can cause fluctuation of T4 or elevated T4 levels. To ensure a thorough assessment, your veterinarian may also check your cat's blood pressure and perform an electrocardiogram, ultrasound, or chest x-ray.

How will my vet treat my cat's hyperthyroidism?

One of several treatment options may be chosen for your cat's hyperthyroidism, based on your pet's case and the advantages and disadvantages of each option. These may include:

Dietary Therapy

  • Anti-thyroid medication, administered orally, to control the disease on either a short-term or long-term basis
  • Radioactive iodine therapy (likely the fastest and most effective treatment option) Surgery to remove the thyroid gland

What is the prognosis for cats with hyperthyroidism?

In most cases, with timely and appropriate treatment, your cat's hyperthyroidism prognosis is positive. However, the prognosis may deteriorate if there are complications with other organs.

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 displaying symptoms of hyperthyroidism? Contact our Lisle vets right away.

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