Hyperthyroidism in Cats: Symptoms & Recommended Diet

Does your cat have hyperthyroidism? Our Lethbridge vets discuss signs, symptoms and diagnosis of this disease. We also recommend what to focus on when it comes to diet. 

Thyroid Hormones & Cat Health

Overactive thyroid glands cause hyperthyroidism in cats - a very common endocrine disorder marked by an increase thyroid hormones being produced. This leads to numerous unhealthy symptoms for your cat. 

Your cat's body uses thyroid hormones to regulate several internal processes and to control the metabolic rate. When too much of this hormone is produced, clinical symptoms can appear quite dramatically and make a cat severely ill. 

Typically, cats suffering from hyperthyroidism burn energy too quickly, leading to weight loss despite the fact that they eat more food. At the same time, their appetite is up. We'll get into more symptoms below.

What causes hyperthyroidism in cats?

For most felines, benign (non-cancerous) changes in the body can trigger the condition. Both thyroid glands are often involved and grow larger (the clinical change is nodular hyperplasia, and it resembles a benign tumour). 

While the cause of this change has not been verified, it's much like hyperthyroidism in humans (its clinical name is toxic nodular goiter). Rarely, a cancerous or malignant tumour named thyroid adenocarcinoma is responsible for the disease. 

What are symptoms of hyperthyroidism in cats?

Older cats between 10 and 13 years old are most likely to suffer from hyperthyroidism. Whether a cat is male or female does not appear to make a significant difference in whether they'll be diagnosed with the disease. 

Hyperthyroidism in cats can cause the following symptoms:

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

You may notice your cat will have a lower tolerance for heat and therefore seek out cooler places to lounge if he or she is experiencing hyperthyroidism. They may also have mild to moderate vomiting and/or diarrhea. 

Though your cat may have a good appetite, they might also grow restless. While both of these signs are common, some cats may feel lethargic or weak, or experience a drop in appetite. Others may pant when they are stressed (an unusual behaviour for cats).

The key is to look out for significant changes in your cat, and to bring them in to your vet for an exam to have them identified, diagnosed and addressed earlier rather than later. 

Clients sometimes ask us, 'Is hyperthyroidism in cats painful?' While the above symptoms usually have a subtle onset as they start, they gradually become more severe as the underlying disease worsens. Other health conditions can also complicate and mask these symptoms, so it's important to see your vet early on. 

How is hyperthyroidism diagnosed?

It can be a challenge to diagnose hyperthyroidism in senior cats. The veterinarian will perform a physical exam for your feline friend and palpate the neck area to look for an enlarged thyroid gland.

A battery of tests might be needed to diagnose a cat with hyperthyroidism, since many other common diseases experienced by senior cats share clinical symptoms with this condition (for example: chronic kidney failure, diabetes, inflammatory bowel disease, intestinal cancer, and more). 

To help rule out diabetes and kidney failure, the veterinarian can take a complete blood count (CBC) and chemistry panel. 

While a simple blood test revealing elevated T4 levels in the bloodstream may be sufficient for a definitive diagnosis, this is not true for 100% of cats due to mild cases of hyperthyroidism or concurrent illnesses. These can both results in fluctuating levels of T4 or showing elevated T4 levels if another illness is influencing the result. 

The veterinarian may also check your cat's blood pressure and perform an ultrasound, chest X-ray or electrocardiogram. 

What are treatments for hyperthyroidism in cats?

We can take a few different approaches to treating this disorder in cats, depending on your animal's specific circumstances and the advantages and disadvantages of each option for your cat's health. Treatment for hyperthyroidism in cats can include:

  • Surgery to remove the thyroid gland
  • Dietary therapy 
  • Radioactive iodine therapy (one of the safest and most effective treatment options)
  • Antithyroid medication, administered orally, to control the disease in either the short-term or long-term (such as methimazole)

What is the best diet for cats with hyperthyroidism?

When it comes to treating hyperthyroidism in cats, diet can play an important role in any treatment plan. Your vet may recommend an iodine-restricted prescription diet. For cats with hyperthyroidism, iodine levels in foods should be limited to 0.32 parts per million or less. 

The thinking behind this is that since adequate iodine intake is needed to produce thyroid hormones, strictly reducing iodine in a cat's diet limits the amount of thyroid hormone that will be produced. 

Generally, cats with overactive thyroid glands need a high-calorie diet with plenty of animal-based protein and enough fat to reduce the rate of muscle wasting and weight loss that come with the disease.

However, if your cat's kidney function is compromised, they may need more moderate protein levels since eating too much protein can lead to a worsening of kidney disease symptoms. Speak to your vet about the best options for your cat. 

Your vet may recommend special canned cat food, but your pet shouldn't need other specific vitamins or minerals.

It's important to note that cats who are on an iodine-restricted diet for hyperthyroidism cannot be fed anything other than their prescription food. This means absolutely no human food, hunting, scavenging or treats. Avoiding products such as supplements and flavoured medications can also help.

What is the prognosis for cats with hyperthyroidism?

With appropriate therapy administered early on, prognosis for hyperthyroidism in cats is generally good. In some cases, complications with other organs can worsen the prognosis. 

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 signs of hyperthyroidism? Contact our veterinary hospital right away to schedule an exam. Our vets can provide diagnosis and treatment for Lethbridge pets.

(403) 328-0028