Carpal tunnel syndrome is an irritation of the median nerve in the wrist that leads to numbness, tingling, pain, and weakness in the hand. The syndrome typically affects the thumb, index, and middle fingers and is often particularly troublesome at night. The median nerve travels down the forearm and enters the hand after passing through the wrist tunnel (carpal tunnel) that is located in the central part of the wrist. Carpal tunnel syndrome affects a low percent of the population and is most common in middle-aged women. Any condition that causes increased direct pressure on the median nerve in the wrist can lead to carpal tunnel syndrome. Many people with carpal tunnel syndrome have no identifiable cause. Carpal tunnel syndrome is diagnosed based on the complaints of the individual combined with physical tests and often electrical tests. No single test is definitive for diagnosis of carpal tunnel syndrome. Rather, the person's complaints and test findings together lead to its diagnosis.