Diet for Cats with Hyperthyroidism

How Thyroid Hormones Affect Your Cat's Health

Hyperthyroidism in cats is the result of overactive thyroid glands. It’s a very common disorder characterized by an increase in the production of thyroid hormones, leading to a variety of unhealthy symptoms for your cat.

Thyroid hormones are used to regulate many processes in the body and to control the metabolic rate, and when too much of the hormone is produced, clinical symptoms can be quite dramatic and make cats severely sick.

Cats suffering from hyperthyroidism tend to burn energy too quickly, which results in weight loss despite eating more food and experiencing an increase in appetite. We’ll discuss more symptoms below.

Spotting The Symptoms of Hyperthyroidism in Cats

Hyperthyroidism is most often seen in older cats between 10 - 13 years of age. There does not appear to be any difference in the number of male cats diagnosed with hyperthyroidism vs the number of female cats with the disease.

Hallmark signs of hyperthyroidism that cat parents should watch for include:

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

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

In advanced cases, some cats may pant when they are stressed (an unusual behavior for kitties). While we note that most cats have a good appetite and are restless, some may feel weaker, lethargic or have a lack of appetite. The key is to watch for significant changes in your cat, and have them addressed earlier rather than later.

These symptoms are usually subtle to start and gradually become more severe as the underlying disease gets worse. Other diseases can also complicate and mask these symptoms, so it’s important to see your vet early.

Causes of Hyperthyroidism in Cats

For most kitties, benign (non-cancerous) changes in their bodies can trigger the condition. Both thyroid glands are most often involved and become enlarged (the clinical change is nodular hyperplasia, and it resembles a benign tumor).

Though we’re not sure what causes the change, it is much like hyperthyroidism in humans (clinically named toxic nodular goiter). Rarely a cancerous (malignant) tumor called thyroid adenocarcinoma is the underlying cause of this disease.

Long-Term Complications Experienced By Cats With Hyperthyroidism

Hyperthyroidism can impact the function of the heart if left untreated, changing the organ’s muscular wall and increasing heart rate, often resulting in heart failure.

High blood pressure (hypertension) is also commonly seen in cats suffering from hyperthyroidism. Though we see this less often, it can result in damage to several organs, including the brain, kidneys, heart and even the eyes. If your vet diagnoses your cat with hypertension in addition to hyperthyroidism, medication will be required to control blood pressure.

Hyperthyroidism and kidney disease often occur at the same time, as they are both commonly seen in older cats. When both these conditions are present, they need to be closely monitored and managed, as managing hyperthyroidism may sometimes adversely affect kidney function.

Diagnosing Hyperthyroidism in Cats

Diagnosing hyperthyroidism in senior cats can be challenging. Your vet will complete a physical exam and palpate your cat’s neck area to look for an enlarged thyroid gland. A battery of tests may be required 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 showing elevated T4 levels in the bloodstream may be enough 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 levels of T4 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.

Treatment for Cats With Hyperthyroidism

There are a few different approaches to treating this condition in cats. Your vet will recommend the best treatment for your kitty based on your pet’s specific circumstances and the advantages and disadvantages of each option. Your cat's treatment for hyperthyroidism may include:

• Radioactive iodine therapy (likely the safest and most effective treatment option)
• Antithyroid medication, administered orally, to control the disease for either the short-term or long-term
• Surgery to remove the thyroid gland
• Dietary therapy

Diet for Cats with Hyperthyroidism

Hyperthyroidism in cats can often be managed through an iodine-restricted prescription diet from your vet. Iodine intake is necessary for the production of thyroid hormones, so the goal of an iodine-restricted therapeutic diet is to help reduce the production of thyroid hormones by reducing iodine in your cat's diet.

Strict adherence to the low-iodine diet is necessary for this treatment to be effective, which can prove challenging for some pet parents and their cats. Along with feeding your cat a prescription food, you will need to strictly monitor your cat's treats and prevent your cat from hunting for their own meal while outside.

Some studies show that after three weeks of following a prescription hyperthyroidism diet, levels of thyroid hormones begin to decrease, and within a few months, they may even return to normal levels.

Prognosis For Cats With Hyperthyroidism

Your kitty’s prognosis for hyperthyroidism will generally be good, with appropriate therapy administered early. 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.