Hyperthyroidism in Cats: Methimazole as a Treatment Option

Hyperthyroidism is a very common disease in cats, most commonly affecting middle-aged to older cats.

Symptoms and Diagnosis of Hyperthyroidism in Cats

Hyperthyroidism is caused when an enlarged thyroid gland (located in a cat’s neck) is producing an excess of thyroid hormones (T3 and T4). When produced properly thyroid hormones help regulate and control normal bodily function. When produced in excess, these hormones can cause many problems.

Weight loss and increased appetite are among the most common symptoms of hyperthyroidism. Affected cats may experience increased thirst and urination as the disease progresses. Hyperthyroidism may also cause vomiting, diarrhea, hyperactivity, unkempt appearance and increased shredding.

Veterinarians presented with a cat exhibiting these symptoms may likely start with a physical exam of the cat, including palpating the cat’s neck to check for an enlarged thyroid gland. A definitive diagnosis of hyperthyroidism may be made based on results from a simple blood test that shows elevated T4 levels in the bloodstream, but veterinarian’s may choose to run additional blood work, chemistry tests to evaluate other bodily functions, electrolyte tests, urinalysis to evaluate kidney function, and others based on the cat’s age and overall health.

Treatment Options for Hyperthyroidism: Medication (Methimazole), Radioactive Iodine Therapy, Surgery and Diet

Treatment for hyperthyroidism in cats is relatively straightforward, with four main approaches; administration of medication (Methimazole), radioactive iodine therapy, surgery and dietary therapy.

The most common approach is generally medication. Many veterinarians prescribe Methimazole which will help reduce the production of the cat’s thyroid hormone. Methimazole does not however, reduce the size of the cat’s thyroid; it just disrupts the production of the hormone itself. Methimazole is readily available from veterinary specific pharmacies and is relatively inexpensive. Methimazole has long been administered orally in a pill form, but has more recently been accepted in flavored liquid or chew form, as well as in a non-oral, transdermal gel that is applied directly to the cat’s skin. Regardless of form, hyperthroid cats will need to be monitored regularly to ensure efficacy and correct dosage.

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Radioactive iodine therapy is considered a safe and effective way to treat Hyperthyroidism, offering a permanent cure. Radioactive iodine, administered by injection is absorbed into the bloodstream and destroys the abnormal thyroid tissue. This specialized treatment is only performed in specialized, licensed facilities and does require hospitalization for the cat until radiation levels have fallen to within acceptable limits. Because of the specialization of treatment and the consequential hospitalization this treatment method can be cost prohibitive.

Surgical removal of the growth(s) of the thyroid gland is also a treatment option in some cases. This surgery requires general anesthesia, which may be an additional risk for older cats. A veterinarian can evaluate whether or not this is a viable option.

The last treatment option is still being evaluated. However, certain case studies suggest that in some hyperthyroid cats, limiting the amount of iodine in the diet may be helpful. There are some concerns about the effects of long-term iodine restrictions in cats, so research is ongoing.

Prognosis of Hyperthyroidism in Cats

Cats can still maintain a good quality of life after being diagnosed with Hyperthyroidism, with appropriate care. It is still unclear as to what exactly causes hyperthyroidism, so prevention is difficult. With regular veterinary well-checks and preventative blood work, veterinarians and pet owners can usually spot the symptoms early and with early diagnosis and treatment, cats can generally avoid secondary problems such as heart disease and high blood pressure. For more information on Hyperthyroidism talk to your veterinarian as they are your best partner in the health of your individual cat.



This information was adapted from information from the following sites: