What is hyperthyroidism in cats?
Overactive thyroid glands cause hyperthyroidism in cats. This very common endocrine disease is marked by an increase in the production of thyroid hormones, which leads to a variety of symptoms that can make your cat severely ill.
Thyroid hormones regulate many processes throughout the body and control the metabolic rate. When too much hormone is produced, clinical symptoms can be quite dramatic.
Cats with hyperthyroidism tend to burn energy too quickly, leading to weight loss even though your kitty is eating more food due to increased appetite. We'll discuss more symptoms below.
What are the symptoms of hyperthyroidism in cats?
Hyperthyroidism is typically diagnosed in older cats between 10 and 13 years of age. A cat's gender doesn't appear to be a factor in whether they develop hyperthyroidism.
Common symptoms of hyperthyroidism in cats include:
- Increased restlessness or irritability
- Poor grooming habits
- Increase in heart rate
- Increase in thirst
- A healthy or increased appetite
- Anxiety or nervousness
- Vomiting or diarrhea
- Vocalizing
Not all cats with hyperthyroidism display the same symptoms. These signs are also usually subtle at the onset of hyperthyroidism and gradually become worse as the disorder progresses.
Other diseases can also complicate and mask these symptoms. This is why it's important to book an appointment for a physical exam with your vet when you first start noticing physical or behavioral changes in your cat so that any abnormalities can be addressed earlier rather than later.
How is hyperthyroidism diagnosed in cats?
Diagnosing hyperthyroidism in senior cats can be challenging. Your vet will complete a physical exam and palpate your cat’s neck 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.
Blood tests and diagnostic imaging such as a chest X-ray, electrocardiogram or ultrasound may also be required.
How to Treat Hyperthyroidism in Cats
When looking at hyperthyroidism in cats, the treatment options can vary. Before settling on a treatment plan, the veterinarian will assess your feline friend's specific needs and circumstances and weigh the advantages and disadvantages of each of the four options: radioactive iodine therapy, medication, surgery, and dietary therapy.
Radioactive Iodine Therapy
Also referred to as I-131 therapy, radioactive iodine therapy is likely the safest and most effective treatment option. The body requires iodine to produce T3 and T4, two important thyroid hormones.
During treatment sessions, your veterinarian will inject radioactive iodine into your cat's body. The iodine goes through the bloodstream to the thyroid gland, where radiation destroys abnormal thyroid tissue without destroying surrounding tissue or disturbing the parathyroid glands. Most cats treated with radioactive iodine have normal hormone levels within one to two weeks of treatment.
While radioactivity carries no significant risk for the treated cat, you and anyone in close contact with your cat must take precautionary protective measures. Your cat must stay in the hospital for three to five days after treatment. Due to strict treatment guidelines, most facilities will not allow visitors during this quarantine period.
Also referred to as I-131 (radioiodine) therapy, this form of nuclear medicine is highly successful at curing hyperthyroidism in cats with only one treatment. In rare cases, some cats may need a second treatment.
Antithyroid Medication
Anti-thyroid drugs curb the production of thyroxine by blocking reactions that trigger the production of the hormone. You would need to administer pills orally twice a day. Your vet will need to examine your cat periodically to check hormone levels and adjust the dosage if necessary.
While these drugs are usually effective, they may be required for the rest of your cat's life. There is also the risk of adverse reactions (as with any drug), which include liver problems, facial swelling and itching, loss of appetite, bleeding, vomiting, and depression. Long-term use is discouraged because the thyroid tumor continues to grow, and these medications may eventually stop working.
Dietary Therapy
Some studies have suggested that for some cats with hyperthyroidism, restricting the amount of iodine in the diet decreases the production of thyroxine by the thyroid gland by limiting the amount of iodine needed for thyroid hormone production. While this diet may help treat this disease, cats must eat only this diet for the rest of their lives without supplementation with other foods, treats, or hunting.
Your vet may consider dietary therapy if your cat has other health conditions that make other treatments impossible.
However, there is some debate around this treatment option, as the effects of long-term iodine restriction can negatively impact overall health. It's also possible that this option won't have the desired effect, and your cat's hyperthyroidism symptoms may even worsen. Consult your veterinarian about these issues if you're considering dietary iodine restriction as a treatment for your cat's disease.
Surgical Treatment
Surgically removing the thyroid glands (thyroidectomy) is a relatively straightforward procedure with a fairly good success rate. Surgery can often eliminate symptoms for the long term or permanently cure the disease, eliminating the need for long-term medication.
However, surgery does come with risks. The parathyroid glands are close to or within the thyroid gland and could be inadvertently damaged during surgery. Because these glands are important for maintaining stable blood calcium levels, damage can negatively affect your cat's long-term health. Medication and radioactive iodine therapy are just as effective and less invasive at treating hyperthyroidism in cats. Surgery is rarely recommended for treating this condition.
What are the dangers of untreated hyperthyroidism?
Left untreated, hyperthyroidism can affect the function of the heart, change the organ's muscular wall and increase heart rate. This often results in heart failure.
Cats with hyperthyroidism often experience high blood pressure (hypertension). Though we see this less often, hypertension can damage several organs, including the heart, brain, kidneys, and even the eyes. If your vet diagnoses your cat with hypertension in addition to hyperthyroidism, medication will be needed to regulate blood pressure.
How long can a cat live with hyperthyroidism?
Feline hyperthyroidism requires long-term treatment and management. That said, the prognosis for cats with this disease is generally good with appropriate therapy. However, any damage to other organs caused by hyperthyroidism can reduce your cat's longevity.
All treatment options carry the risk of potential hypothyroidism, which requires daily thyroid hormone supplementation.
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.