Carpal Tunnel Syndrome

Anatomy

The median nerve is centrally located in the forearm and wrist.  It controls sensation to the underside of the thumb, index, and middle fingers, as well as half of the ring finger.  It also helps control movement of small muscles of the thumb.  At the base of the palm, the median nerve runs through the carpal tunnel, a passageway surrounded by small wrist bones on the underside and a tough ligament just beneath the palm.  It is a small, relatively unyielding space.  Swelling or increased pressure inside the tunnel can compress or injure the nerve.

Symptoms

Symptoms of carpal tunnel syndrome include pain, numbness, tingling or burning in the palm or fingers.  The thumb, index and middle fingers are most commonly affected.  The ability to distinguish between the feeling of hot and cold can be lost.  Carpal tunnel sufferers may feel as if their hands are swollen when little to no swelling is apparent to an observer.  Symptoms of carpal tunnel syndrome are often most frequent at night.  There may be a positional component, as shaking out the hand may bring relief.

As carpal tunnel syndrome progresses, similar symptoms may be experienced during the daytime.   Motor symptoms also emerge, including decreased grip strength, difficulty grasping small items or frequent dropping of objects.  Atrophy or wasting of muscles at the base of the thumb can be seen in chronic or untreated cases.  At its most severe, carpal tunnel syndrome can be quite disabling.  Seemingly simple tasks, such as tying shoes, buttoning a blouse or opening a jar can become prohibitively difficult.

Causes

Carpal tunnel syndrome can be caused by a combination of factors, including fracture or other types of wrist trauma that result in swelling, hypothyroidism, rheumatoid arthritis, wrist tumor and fluid retention that can develop during pregnancy or menopause.  The common thread is the development of increased pressures on the median nerve in the carpal tunnel.  Metabolic diseases, such as diabetes, have a direct effect on nerves and make them much more susceptible to compression injury.  Exposure to vibration, as with repetitive use of vibrating hand tools or machinery, is also a contributing factor.  Women are at least three times more likely than men to develop carpal tunnel syndrome.

There is no convincing scientific evidence that proves whether repetitive and forceful movements of the hand and wrist during work or leisure activities can cause carpal tunnel syndrome. However, the risk of developing carpal tunnel syndrome is increased in certain occupations, particularly assembly line work.  Despite popular perception that keyboarding “causes” the problem, a 2001 study by the Mayo Clinic found heavy computer use of up to 7 hours a day did not increase a person's risk of developing carpal tunnel syndrome.  Carpal tunnel syndrome has been shown to be three times more common among assemblers than among data-entry personnel.

Diagnosis

Early diagnosis and treatment of carpal tunnel syndrome are important to avoid permanent damage to the median nerve. Other problems that may mimic carpal tunnel syndrome should be excluded.  Your physician should take a thorough history and perform a physical examination.  The best objective diagnostic test for carpal tunnel syndrome remains electrodiagnostic testing (See Nerve Function Testing).  This includes nerve conduction studies, in which electrical pulses activate specific upper extremity nerves to provide an assessment of median nerve function and to determine whether any focal nerve entrapment exists. Electromyography (EMG) involves direct muscle recording to assess health and function of the nerve supply to that muscle.  The age and severity of any nerve injury can be determined in this way.

Treatment

Treatment of carpal tunnel syndrome generally proceeds in step-wise fashion, depending on the severity of the condition and the response to previous treatments.  Relative rest of the affected wrist is usually a good initial strategy.  The wrist can be immobilized each night.  Depending on symptoms and work tolerance, splinting can be carried over to daytime hours.  Oral anti-inflammatory medications, diuretics or oral steroids may be of short-term benefit.  Some studies show that vitamin B6 may provide some symptom relief.

Rehabilitation helps to address the physical and ergonomic factors that may contribute to overuse.  Physical and occupational therapists instruct patients in methods to achieve relative rest throughout the day, especially when patients must do repetitive hand motion.  Stretching may play a beneficial role in symptom management, while yoga appears to reduce pain and improve grip strength.

If these measures have not worked, carpal tunnel steroid injection is often the next step.  In addition to providing symptom relief, steroid injection has been shown to produce an overall improvement in median nerve function.  The duration of pain relief following injection varies, but can last for several months at a time.

If non-surgical treatment is ineffective or if electrodiagnostic testing shows the median nerve injury to be severe, surgery is a reasonable option.  It has become one of the most commonly performed surgical procedures in the US.  Surgery can be done as an open or an endoscopic procedure.  Although symptoms may be relieved immediately following surgery, full recovery may take several months.  Surgical outcome data are generally favorable, but symptoms can recur over time.