In the wrist, nerves and tendons pass through a space called the carpal tunnel.
Because the carpal tunnel is somewhat narrow, a major nerve called the median nerve that passes through this tight space, can become irritated or compressed. Carpal tunnel syndrome is a combination of numbness, tingling, pain and weakness in the hand caused by compression of the median nerve in the carpal tunnel.
Symptoms tend to show up most in the thumb, index finger, middle finger and half of the ring finger because the median nerve provides sensation to those areas.
Because the carpal tunnel already is narrow, the nerve can become irritated if it narrows even a little more. Injury to the nerve also can cause carpal tunnel syndrome. There are several common causes, including:
Arthritis or fracture near the wrist
Overuse (as in typists, cashiers or certain athletes)
Thyroid disease, particularly an underactive thyroid
Often, carpal tunnel syndrome occurs without a clear reason. The condition affects women more often than men, perhaps because women normally have smaller carpal tunnels. It can occur in one or both hands.
Symptoms of carpal tunnel syndrome can include:
Burning, tingling or numbness of the fingers
Difficulty gripping and hold tools, pens, eating utensils and other objects
Problems making a strong fist
Symptoms may appear first at night and are most noticeable in the thumb and the index and middle fingers. People with carpal tunnel syndrome often describe awakening with a tingling sensation and the need to shake out the hands to recover normal feeling. There can be pain in the wrist that radiates into the hand or into the forearm. If the condition is not treated, the muscles of the thumb can waste away so that the normal mound of muscles at the base of the thumb eventually flattens.