Hyperthyroidism is a common disease in middle-aged to older cats. It is most often caused by a benign (non-cancerous) thyroid tumor that produces thyroid hormones in excess; much less commonly, a malignant (cancerous) thyroid tumor is responsible for the over-production of these thyroid hormones. Thyroid hormones help to regulate vital functions of most organs, including but not limited to the brain, musculoskeletal system, digestive system, and heart. Excess thyroid hormones can cause numerous clinical signs, but the most common are weight loss, increased appetite, and increased thirst and urination. Vomiting, diarrhea, and hyperactivity are also possible. More severe complications of hyperthyroidism include high blood pressure and heart disease.

Hyperthyroidism may be suspected based on the pet’s age, physical exam findings, and clinical signs noted at home. In some cats, palpation of the neck may reveal an enlarged thyroid gland. Often these cats are also thin and may have an unkempt haircoat.

A diagnosis of hyperthyroidism, however, requires a test that measures the level of thyroid hormones in the blood. In addition to a thyroid test, full blood work and urine testing are frequently advised, as thyroid disease can affect other organs. If your vet suspects secondary heart disease, referral to a veterinary cardiologist may be recommended.

There are several treatment options for hyperthyroidism, including medication, radioactive iodine therapy, surgery, and prescription diets. After obtaining a diagnosis, assessing other organ function, and determining the severity of your pet’s clinical signs, your primary care veterinarian or an internal medicine specialist will be able to help you choose the best treatment option for your pet.