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What Is & How to Treat Hyperthyroidism in Cats

Older cats sometimes develop hyperthyroidism. Today, our Voorhees vets explain the symptoms, diagnosis, and treatment options for this disorder. 


What is hyperthyroidism in cats?

Your cat's thyroid glands are in its neck. If these glands become overactive, this results in hyperthyroidism, a common endocrine disorder in kitties. 

Many processes throughout the body are regulated by thyroid hormones, which also control the metabolic rate. When too many of these hormones are produced, the metabolism is accelerated, which negatively impacts almost every organ in the cat's body (including the heart and kidneys). This can also cause cats to suffer from severe clinical symptoms and illnesses. 

Felines with hyperthyroidism tend to burn energy to quickly, which leads to weight loss even though your cat will have a heartier appetite and be eating more food. 

Cats diagnosed with hyperthyroidism are usually middle-aged (8 or older). Most are older than 10 years – between 12 and 13 – at the onset of this condition. Male and female cats are affected in equal numbers. 

Iodine treatment (I-131 therapy) is often prescribed for cats with hyperthyroidism. Below, you'll find more symptoms of and treatment options for the disorder. 

What are symptoms of hyperthyroidism in cats?

Common symptoms of hyperthyroidism in cats include:

  • Increased irritability or restlessness
  • Increase in thirst
  • Poor grooming habits 
  • Irregular or rapid heartbeat 
  • Typically a healthy or increased appetite 

Some cats may also suffering from mild to moderate diarrhea and/or vomiting, while others will seek cool places to lie (such as a bathtub or bathroom floor) due to their low tolerance for heat. 

If the disease has progressed significantly, your cat may also pant when stressed (an unusual ehavior for our feline friends). While most cats will have a healthy appetite and stay active, some may appear to lack appetite, or be weak or lethargic. Taking note of any significant changes in your cat's behavior and demeanor will be key. If you do notice any changes, make an appointment with your vet to have the symptoms addressed as soon as possible. 

These symptoms usually appear subtle in the disorder's early stages and gradually become more severe as the underlying disease worsens. Other diseases can also mask and complicate symptoms of hyperthyroidism, so seeing your vet early is important. 

What causes hyperthyroidism in cats? 

In most cases, this condition is triggered by benign (non-cancerous) changes in the body. Both thyroid glands are typically involved and become enlarged. This clinical name for this process is called hyperplasia, which resembles a benign tumor. 

While we aren't sure precisely what causes these changes, it is similar to hyperthyroidism in humans (clinically referred to as toxic nodular goiter). Occasionally, the disorder is caused by a malignant (cancerous) tumor named thyroid adenocarcinoma. 

What are the long-term complications of hyperthyroidism?

Left untreated, hyperthyroidism can affect how the heart works, changing the organ's muscular wall and increasing the heart rate. It can eventually lead to heart failure. 

Hypertension (high blood pressure) is another potential complication of hyperthyroidism. While this is a less common occurrance, it can cause damage to several organs, including the heart, kidneys, eyes, and even the brain. If your veterinarian diagnoses your cat with hyperthyroidism, medication will be required to control your kitty's blood pressure. 

While hyperthyroidism and kidney disease often occur at the same time, they are both commonly diagnosed in older cats. When both of these conditions are present, your vet will need to monitor them closely, as managing hyperthyroidism can sometimes adversely affect kidney function. 

How is hyperthyroidism in cats diagnosed? 

If you suspect your cat may have hyperthyroidism, contact your veterinarian right away to book an exam.

During your cat's physical exam, the vet will feel your cat's neck for an enlarged thyroid gland and check for clinical signs of the condition. Your kitty's medical history will also be taken into consideration. 

A battery of tests will likely be needed to diagnose hyperthyroidism in your cat, as many other common diseases experienced by 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 demonstrating elevated T4 levels in the bloodstream may be sufficient for a definitive diagnosis, though this is not true for 100% of cats due to concurrent illnesses or mild cases of hyperthyroidism, which can result in fluctuating T4 levels 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.We may also refer you to a veterinary specialist for diagnosis and treatment, if required. 

What are treatment options for 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. 

Radioactive iodine treatment (also referred to as I-131 therapy and radio-iodine treatment) is frequently prescribed for cats with hyperthyroidism This is often 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

How long do cats with hyperthyroidism live?

Most cats that are diagnosed with hyperthyroidism and have this disorder treated with effective medical management will live an average of three to five years before dying of either heart failure or kidney failure. However, those three to five years can still provide lots of good, quality time with their owners. 

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 vets at Voorhees Veterinary Center to schedule an examination for your feline companion.

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