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What is hyperthyroidism in cats? How is it treated?

What is hyperthyroidism in cats? How is it treated?

Middle-aged and senior cats may experience hyperthyroidism as they age. In this post, you will learn about the causes of hyperthyroidism in cats, the symptoms of the disease 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 the 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 Miller Clark Animal 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.

What is the best treatment for hyperthyroidism in cats? 

Following diagnosis, the next question will be how to treat hyperthyroidism in cats. Based on your pet's unique circumstances and the advantages and disadvantages of each option, your vet may recommend one of several treatment options for your feline friend's hyperthyroidism. 

Some veterinarians offer radioactive iodine treatment (also referred to as I-131 therapy and radio-iodine treatment) for cats with hyperthyroidism. This may be the safest and most effective treatment option for this disease. 

Other treatment options may include:

  • 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 should you feed a cat with hyperthyroidism?

Hyperthyroidism in cats can often be managed with a therapeutic diet prescribed by a veterinarian. This iodine-restricted diet aims to decrease the production of thyroid hormones in your cat's body since thyroid hormones require iodine for their production. 

If your cat is diagnosed with hyperthyroidism, your vet may recommend a change in diet or prescribe specially formulated food to help manage the condition. 

How long do cats with hyperthyroidism live?

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. Please make an appointment with your vet for an accurate diagnosis of your pet's condition.

Is your cat showing signs of hyperthyroidism? Contact our Mamaroneck vets today to book an examination for your feline family member.

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