Vet Med, 2004. 99(11): p.951-954.
Since it was first documented in 1979, hyperthyroidism has become increasingly more common in cats. It is now the most commonly diagnosed endocrinopathy in cats. This may be a true increase in disease incidence, or it may be attributable to other factors, such as the longer life spans of cats or better detection by veterinarians. Hyperthyroidism is characterized by increased serum concentrations of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). The increases in serum thyroid hormone concentrations are usually the result of benign adenomatous hyperplasia of the thyroid glands. In less than 2% of the cases, the hyperthyroidism is caused by thyroid adenocarcinoma. Ectopic thyroid tissue may be present as well, which may have implications for the type of treatment chosen. No specific etiologies have been identified, but environmental and genetic factors have been studied to help explain the increase in the incidence of hyperthyroidism over the past few decades.