Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) occurs when the median nerve, which runs from the forearm into the palm of the hand, becomes pressed or squeezed at the wrist.  The carpal tunnel—a narrow, rigid passageway of ligament and bones at the base of the hand—houses the median nerve and the tendons that bend the fingers.  The median nerve provides feeling to the palm side of the thumb and to the index, middle, and part of the ring fingers (although not the little finger).   It also controls some small muscles at the base of the thumb.

Sometimes, thickening from the lining of irritated tendons or other swelling narrows the tunnel and causes the median nerve to be compressed.  The result may be numbness, weakness, or sometimes pain in the hand and wrist, or occasionally in the forearm and arm.  CTS is the most common and widely known of the entrapment neuropathies, in which one of the body’s peripheral nerves is pressed upon.

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Symptoms usually start gradually, with frequent burning, tingling, or itching numbness in the palm of the hand and the fingers, especially the thumb and the index and middle fingers. Some carpal tunnel sufferers say their fingers feel useless and swollen, even though little or no swelling is apparent. The symptoms often first appear in one or both hands during the night, since many people sleep with flexed wrists. A person with carpal tunnel syndrome may wake up feeling the need to "shake out" the hand or wrist. As symptoms worsen, people might feel tingling during the day. Decreased grip strength may make it difficult to form a fist, grasp small objects, or perform other manual tasks. In chronic and/or untreated cases, the muscles at the base of the thumb may waste away. Some people are unable to tell between hot and cold by touch.

Carpal tunnel syndrome is often the result of a combination of factors that reduce the available space for the median nerve within the carpal tunnel, rather than a problem with the nerve itself.   Contributing factors include trauma or injury to the wrist that cause swelling, such as sprain or fracture; an overactive pituitary gland; an underactive thyroid gland; and rheumatoid arthritis.   Mechanical problems in the wrist joint, work stress, repeated use of vibrating hand tools, fluid retention during pregnancy or menopause, or the development of a cyst or tumor in the canal also may contribute to the compression.  Often, no single cause can be identified.

Women are three times more likely than men to develop carpal tunnel syndrome, perhaps because the carpal tunnel itself may be smaller in women than in men. The dominant hand is usually affected first and produces the most severe pain. Persons with diabetes or other metabolic disorders that directly affect the body's nerves and make them more susceptible to compression are also at high risk. Carpal tunnel syndrome usually occurs only in adults.

The risk of developing carpal tunnel syndrome is not confined to people in a single industry or job, but is especially common in those performing assembly line work - manufacturing, sewing, finishing, cleaning, and meat, poultry, or fish packing. In fact, carpal tunnel syndrome is three times more common among assemblers than among data-entry personnel. 

Early diagnosis and treatment are important to avoid permanent damage to the median nerve.

• A medical history and physical examination of the hands, arms, shoulders, and neck can help determine if the person's discomfort is related to daily activities or to an underlying disorder, and can rule out other conditions that cause similar symptoms.  The wrist is examined for tenderness, swelling, warmth, and discoloration.  Each finger should be tested for sensation and the muscles at the base of the hand should be examined for strength and signs of atrophy.
• Routine laboratory tests and X-rays can reveal fractures, arthritis, and detect diseases that can damage the nerves, such as diabetes.
• Specific tests may reproduce the symptoms of CTS.  In the Tinel test, the doctor taps on or presses over the median nerve in the person's wrist.  The test is positive when tingling occurs in the affected fingers.  Phalen’s maneuver (or wrist-flexion test) involves the person pressing the backs of the hands and fingers together with their wrists flexed as far as possible.  This test is positive if tingling or numbness occur in the affected fingers within 1-2 minutes.  Doctors may also ask individuals to try to make a movement that brings on symptoms.
• Electrodiagnostic tests may help confirm the diagnosis of CTS.  A nerve conduction study measures electrical activity of the nerves and muscles by assessing the nerve’s ability to send a signal along the nerve or to the muscle.  Electromyography is a special recording technique that detects electrical activity of muscle fibers and can determine the severity of damage to the median nerve.
• Ultrasound imaging can show abnormal size of the median nerve.  Magnetic resonance imaging (MRI) can show the anatomy of the wrist but to date has not been especially useful in diagnosing carpal tunnel syndrome.