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Carpal Tunnel Syndrome
Carpal tunnel syndrome occurs when the median
nerve, which runs from the forearm into the
hand, becomes pressed or squeezed at the wrist.
The median nerve controls sensations to the palm
side of the thumb and fingers (although not the
little finger), as well as impulses to some
small muscles in the hand that allow the fingers
and thumb to move. The carpal tunnel - a narrow,
rigid passageway of ligament and bones at the
base of the hand - houses the median nerve and
tendons. Sometimes, thickening from irritated
tendons or other swelling narrows the tunnel and
causes the median nerve to be compressed. The
result may be pain, weakness, or numbness in the
hand and wrist, radiating up the arm. Although
painful sensations may indicate other
conditions, carpal tunnel syndrome is the most
common and widely known of the entrapment
neuropathies in which the body's peripheral
nerves are compressed or traumatized.
What are the symptoms of
carpal tunnel syndrome?
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.
What are the causes of
carpal tunnel syndrome?
Carpal tunnel syndrome is often the result of a
combination of factors that increase pressure on the
median nerve and tendons in the carpal tunnel, rather
than a problem with the nerve itself. Most likely the
disorder is due to a congenital predisposition - the
carpal tunnel is simply smaller in some people than in
others. Other contributing factors include trauma or
injury to the wrist that cause swelling, such as sprain
or fracture; overactivity of the pituitary gland;
hypothyroidism; 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. In some cases no cause can be
identified.
There is little clinical data to prove whether repetitive and forceful movements of the hand and wrist during work or leisure activities can cause carpal tunnel syndrome. Repeated motions performed in the course of normal work or other daily activities can result in repetitive motion disorders such as bursitis and tendonitis. Writer's cramp - a condition in which a lack of fine motor skill coordination and ache and pressure in the fingers, wrist, or forearm is brought on by repetitive activity - is not a symptom of carpal tunnel syndrome. Who is at risk of developing carpal tunnel syndrome?
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. A 2001 study by the Mayo Clinic found heavy computer use (up to 7 hours a day) did not increase a person's risk of developing carpal tunnel syndrome. During 1998, an estimated three of every 10,000 workers lost time from work because of carpal tunnel syndrome. Half of these workers missed more than 10 days of work. The average lifetime cost of carpal tunnel syndrome, including medical bills and lost time from work, is estimated to be about $30,000 for each injured worker. How is carpal tunnel syndrome diagnosed?
Early diagnosis and treatment are important to
avoid permanent damage to the median nerve. A
physical examination of the hands, arms,
shoulders, and neck can help determine if the
patient's complaints are related to daily
activities or to an underlying disorder, and can
rule out other painful conditions that mimic
carpal tunnel syndrome. 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 diabetes, arthritis, and fractures.
Physicians can use specific tests to try to produce the symptoms of carpal tunnel syndrome. In the Tinel test, the doctor taps on or presses on the median nerve in the patient's wrist. The test is positive when tingling in the fingers or a resultant shock-like sensation occurs. The Phalen, or wrist-flexion, test involves having the patient hold his or her forearms upright by pointing the fingers down and pressing the backs of the hands together. The presence of carpal tunnel syndrome is suggested if one or more symptoms, such as tingling or increasing numbness, is felt in the fingers within 1 minute. Doctors may also ask patients to try to make a movement that brings on symptoms. Often it is necessary to confirm the diagnosis by use of electrodiagnostic tests. In a nerve conduction study, electrodes are placed on the hand and wrist. Small electric shocks are applied and the speed with which nerves transmit impulses is measured. In electromyography, a fine needle is inserted into a muscle; electrical activity viewed on a screen can determine the severity of damage to the median nerve. Ultrasound imaging can show impaired movement 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.
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