Hyperthyroidism is very common in middle age to older cats. Hyperthyroidism occurs when the thyroid gland produces excessive levels of thyroid hormone. There are many different signs of hyperthyroidism in the cat with the most common signs being excessive appetite, vomiting, and weight loss. Unfortunately, this disease may show a wide variety of symptoms. Some cats will have symptoms just the opposite of what we consider the most common. In other words, some cats may have weight gain and loss of appetite. Hypothyroidism, in all cases, causes an increase in the blood pressure, which results in damage to the kidneys and eventually causes kidney failure. Because of the wide variety of symptoms and the risk of kidney failure, all cats over seven years should be checked yearly. A simple blood test is used to determine if your cat has hyperthyroidism. The good news is that once a diagnosis has been made, the disease is treatable.