Thyroid Hormones & 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.
What are 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.
What causes 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.
What are the long-term complications of hyperthyroidism?
Hyperthyroidism can impact the function of the heart if left untreated, changing the organ’s muscular wall and increasing heart rate, and 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.
How is hyperthyroidism diagnosed?
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.
How will my vet treat my cat’s hyperthyroidism?
There are a few different approaches to treating this condition in cats. Your vet will recommend the best treatment for your kitty based 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
What is the 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.
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