Feline Hyperthyroidism is a common disease that usually affects cats age 8 and older. Hyperthyroidism is caused by an enlarged thyroid gland that produces too much thyroid hormone, due to a tumor affecting one or both of the glands. In most cases, these tumors are benign; however, in 2% to 5% of cases, they are cancerous. Thyroid hormone affects numerous systems in the body (metabolism, heart, kidneys, and liver), so an unstable thyroid can have disastrous consequences. 

Symptoms of an overactive thyroid include:

• Excessive thirst and urination
• Increased appetite
• Aggressive behavior (or overly energetic)
• Yowling
• Weight loss (despite an increased appetite)
• Vomiting
• Diarrhea
• Muscle Weakness
• Lethargy
• Unkempt coat or hair loss

Your veterinarian will perform a physical exam and a CBC (complete blood count) with a thyroid-specific test known as the T4 panel. During the exam, we may be able to feel the enlarged gland. Your cat's heart rate and blood pressure will also be checked. Cats with hyperthyroidism will have an elevated heart rate and high blood pressure.

The results of the blood test will offer a more complete picture and will also rule out other conditions that can present similar to hyperthyroidism, such as chronic renal failure or liver disease.

There are three basic methods of treating hyperthyroidism: drug therapy, radioactive iodine therapy, and surgery. We will discuss the treatment options and recommend the best one for your cat. Cats with hyperthyroidism can lead normal, happy lives if they receive proper, on-going treatment.