Carpal Tunnel Syndrome

What Is It?

In the wrist, nerves and tendons pass through a space between bones and ligaments called the carpal tunnel.

Because the carpal tunnel is somewhat narrow, the median nerve, a major 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 be most prominent in thumb, index finger, middle finger and half of the ring finger because the median nerve provides sensation to those areas.

Even a small additional narrowing or other injury can lead to nerve irritation. There are several common causes, including:

• Arthritis or fracture near the wrist
• Pregnancy
• Diabetes
• Overuse (as in typists, cashiers or certain athletes)
• Thyroid disease, particularly an underactive thyroid

In each of these conditions, there is either nerve injury or added pressure in the carpal tunnel.

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

Symptoms of carpal tunnel syndrome can include burning, tingling or numbness of the fingers, difficulty gripping tools or other implements, and problems making a 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 eventually can waste away so that the normal "hill" of muscles at the base of the thumb eventually flattens.

Diagnosis

Your doctor will look for decreased feeling in your fingers and for muscle weakness in the affected hand. Your doctor also will check your thumb muscles for signs of wasting and your wrists for signs of arthritis. Your doctor also may look for abnormal accumulation of fluid in several different parts of your body, including your hands, feet and legs, since extra fluid can add pressure in the carpal tunnel.

A wrist examination, looking for arthritis, is an important part of the evaluation. In addition, the examination likely will include maneuvers that test for abnormal nerve function when the pressure in the carpal tunnel is raised. The Tinel's test is performed by tapping over the median nerve at the wrist. In Phalen's maneuver, the wrist is flexed for 30 to 60 seconds. In each of these, the development of radiating pain, numbness or tingling suggests compression of the median nerve in the carpal tunnel.