feline hyperthyroidism

Hyperthyroidism (also called thyrotoxicosis) is one of the most common diseases of the middle-aged and older cat. It is a multi-system disorder caused by an increase in the amount of thyroid hormones (T3 and T4) produced by an enlarged thyroid gland. It was first documented in cats almost 30 years ago but the cause of the disease has been elusive.

SOURCE: cats.consultinghealth.com