Hyperthyroidism in Cats: Symptoms, Diagnosis & Treatments

Middle-aged and senior cats may experience hyperthyroidism as they age. In this post, our Greensboro vets define the disease, symptoms, diagnosis and treatment options.


What is hyperthyroidism in cats?

Hyperthyroidism is a very common disorder that can occur when a cat’s thyroid glands (located in the neck) become overactive and produce too much of the thyroid hormone.

Thyroid hormones control the metabolic rate and regulate many processes in the body. When excessive amounts of this hormone are produced, clinical symptoms can appear and make cats severely ill.

If your cat is suffering from hyperthyroidism, she may tend to burn energy too quickly, resulting in weight loss despite eating more food and experiencing an increase in appetite. More symptoms are explained below.

What are the symptoms of hyperthyroidism in cats?

These symptoms usually appear in cats that are middle-aged and older (most are older than 10 - between 12 and 13 years old - when the disease can become an issue. Male and female cats are equally impacted.

Trademark signs of hyperthyroidism include:

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

Some cats will also have mild to moderate vomiting and/or diarrhea, while others may seek cooler places to nap and have a low tolerance for heat.

In advanced cases, some kitties pant when stressed (an unusual behavior for cats). While most cats are restless and have a good appetite, some may experience a lack of appetite or feel lethargic or weak. It’s critical to look for significant changes in your cat, and have a vet address them earlier rather than later.

These symptoms usually appear in a subtle manner at first and can gradually get worse as the underlying disease progresses. Other diseases may also complicate and mask these symptoms, so you’ll want to see your vet early.

What causes hyperthyroidism?

For most cats, the condition is triggered by benign (non-cancerous) changes in their bodies. Both thyroid glands are typically involved and become enlarged (the clinical change is referred to as nodular hyperplasia, which resembles a benign tumor).

Though it’s not clear what causes the change, it’s much like hyperthyroidism in humans (clinically named toxic nodular goitre). Rarely, a malignant cancerous tumor called thyroid adenocarcinoma is the underlying culprit.

What are long-term complications of hyperthyroidism?

If left untreated, hyperthyroidism can affect the heart’s function, changing this organ’s muscular wall and increasing heart rate. It may eventually lead to heart failure.

High blood pressure, or hypertension, is another potential complication. Though this is not a very common problem, it can lead to several organs being damaged - including the heart, eyes, kidneys and brain. If your cat is diagnosed with hypertension along with hyperthyroidism, your kitty will need medication to control blood pressure.

Kidney disease and hyperthyroidism often occur comorbidly as they are both commonly seen in older cats. When this is the case, they need to be monitored closely and managed, as managing hyperthyroidism can sometimes adversely impact kidney function.

How is hyperthyroidism diagnosed?

Hyperthyroidism can be difficult to diagnose in senior cats. At Guilford-Jamestown Veterinary Hospital, we take a comprehensive approach to internal medicine. Our vets have extensive experience in diagnosing and treating challenging cases.

Your vet will perform a physical exam and palpate your cat’s neck area to look for an enlarged thyroid gland.

The veterinarian will also likely need to complete a battery of tests to diagnose hyperthyroidism in your cat, as several other common diseases senior cats can experience (chronic kidney failure, inflammatory bowel disease, diabetes, cancer and more) share clinical symptoms with hyperthyroidism.

A chemistry panel and complete blood count (CBC) can help eliminate diabetes and kidney failure as causes.

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

Your vet may also check your cat’s blood pressure and complete 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?

Generally, your cat’s prognosis for hyperthyroidism will be good with appropriate therapy, administered early. In some cases, prognosis can worsen 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 Greensboro vets right away.

Hyperthyroidism in cats, Greensboro Vet

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