Feline hyperthyroidism is a systemic disorder caused by excessive thyroid hormone.
Thyroid hormone regulates metabolism, and therefore, affects almost every system in the body. Hyperthyroidism is the most common endocrine disorder diagnosed in cats over 8 years of age. The average age of onset is 12 to 13 years. Advanced cases may show signs such as anorexia, depression and weakness. These are general signs and only raise the suspicion of a thyroid disorder.