Hyperthyroidism is a disorder that occurs most commonly in the middle-aged to old cat. It usually occurs when the thyroid gland develops functional nodules which secrete excessive amounts of thyroid hormones, resulting in signs that reflect an increased metabolic rate.

The most common signs of hyperthyroidism include weight loss, hyperexcitability, increased appetite, increased water drinking, and increased urination. Often owners remark that their cat appears to be experiencing a second kittenhood. Gastrointestinal signs also are common and may include vomiting, diarrhea, and increased volumes of feces. Cardiovascular signs may include increased heart rate, murmurs, labored breathing, and even congestive heart failure.

Your cat should be brought to your veterinarian for an examination if showing any of the above signs. If your veterinarian suspects hyperthyroidism, he or she will recommend a blood test to find out if there are elevated serum concentrations of the thyroid hormones. If hyperthyroidism is diagnosed, your veterinarian will recommend the appropriate course of action for your particular cat. The key is to realize that your cat has a problem and that steps should be taken to address it.

The writers are Dr. Steven B. Holzman, Dr. William R. Haagenson and Dr. Kathleen Tapley. They are associated with the Nassau-Suffolk Veterinary Hospital of Farmingdale.