What is carpal tunnel syndrome?

Causes and Symptoms

The carpal tunnel is a narrow passage of ligament and bones that contains the median nerve and tendons. Carpal tunnel syndrome, also known as median nerve palsy, is caused by the transverse carpal ligament compressing the median nerve. This nerve passes through the carpal tunnel alongside nine tendons attached to the muscles that enable the hand to close and the wrist to flex. The tendons have a lubricating lining called the synovium, which normally allows the tendons to glide back and forth smoothly through the tunnel during wrist and hand movements. The median nerve is the softest component within the tunnel and becomes compressed when the tendons are stressed and become swollen. Median nerve compression most often results when the synovium becomes thick and sticky as a result of the wear and tear of aging or repeatedly performing stressful motions with the hands while holding them in the same position for extended periods. The carpal tunnel is smaller in some people than in others, predisposing them to carpal tunnel syndrome. Entrapment of the median nerve is less commonly caused by rheumatoid arthritis, diabetes mellitus, poor thyroid gland or pituitary function, excessive fluid retention during pregnancy or menopause, medications, vitamin B6 or B12 deficiency, or bone protruding in the tunnel from previous dislocations or fractures of the wrist.

Initial symptoms of carpal tunnel syndrome include tingling and numbness in the hands, often beginning in the thumb and index and middle fingers, that causes the hand to feel as though it were asleep and shooting pain from the thenar region radiating as far up as the neck. Later symptoms include burning pain from the wrist to the fingers, changes in touch or temperature sensation, clumsiness in the hands, and muscle weakness creating an inability to grasp, pinch, and perform other thumb functions. Swelling of the hands and forearms and changes in sweat gland functioning in the hands may also be noted. Symptoms can be intermittent or constant and often progress to the point of regularly awakening the patient at night. Temporary relief is sometimes available by elevating, massaging, and shaking the hand. Although very treatable if diagnosed early, carpal tunnel syndrome can escalate into persistent pain, which can become so crippling that workplace duties and such simple tasks as holding a cup, writing, and buttoning a shirt are compromised. Carpal tunnel syndrome usually occurs in adults and is more common in women than in men.

A clinical examination for confirmation of median nerve impingement includes wrist examination, an X-ray for previous injury and arthritis, and assessment of swelling and sensitivity to touch or pinpricks. Tapping of the median nerve (Tinel’s test) will cause tingling or shocklike sensations in the fingers. Holding the wrist in a flexed position for several minutes with the heel of the hands touching for several minutes (Phalen’s test) will result in tingling or numbness in the hands. Nerve conduction tests, which measure nerve transmission speed by electrodes placed on the skin, and electromyogram evaluation, which notes muscle function abnormalities, may also assist in a diagnosis. Ultrasound identifies whether motion of the median nerve is impeded.

Treatment and Therapy

Early diagnosis and the taking of appropriate preventive measures, such as ergonomic modifications in the way that upper extremity movements are performed, often reduce the risk of developing advanced carpal tunnel syndrome. The need to compensate for weak muscles with an inappropriate wrist position can be reduced by maintaining a neutral (straight) wrist position instead of a flexed, extended, or twisted wrist position; utilizing the entire hand and all the fingers to grasp and lift objects, instead of gripping solely with the thumb and index finger; minimizing repetitive movements; allowing the upper extremities regular rest periods; using power tools, instead of hand tools; alternating work activities; switching hands; reducing movement speed; and stretching and using strengthening exercises for the hand, wrist, and arm. Keeping the hands warm to maintain good blood circulation and avoiding smoke-filled environments, which reduce peripheral blood flow, are also recommended.

Treatment generally begins with splinting of the wrist and medication, but surgery may be required if symptoms do not subside within six months. Both nocturnal splints and job-specific occupational splints can effectively keep the wrist in a neutral position, thus avoiding the extreme wrist flexion or extension that narrows the carpal tunnel. Wrist supports lying on the desk in front of a computer keyboard are often helpful, but the benefit of strapping on wrist splints while typing is controversial because disuse atrophy may result, potentially creating a muscle imbalance. Aspirin and other oral nonsteroidal anti-inflammatory drugs (NSAIDs) may reduce swelling and inflammation, relieving some nerve pressure. Corticosteroids and cortisone-like medications injected directly into the carpal tunnel can help confirm diagnosis if the symptoms are relieved. Diuretics and vitamin supplementation may also be beneficial. Vitamin B6 has shown promise in reducing the symptoms of carpal tunnel syndrome. Exercises can be performed, under the guidance of a physical or
occupational therapist, to stretch and strengthen the wrists. Acupuncture and chiropractic may benefit some who suffer from carpal tunnel syndrome; however, their effectiveness has not been supported. Pain reduction and improved grip strength have been documented among patients who practice yoga.

If initial symptoms do not subside, pain increases, or the risk of permanent nerve and muscle damage exists, then surgery may be necessary, with subsequent rehabilitation and ergonomic counseling with a physical or occupational therapist. Carpal tunnel release is one of the most common surgical procedures in the United States. It is often recommended for individuals who experience carpal tunnel symptoms for more than six months. This outpatient surgical procedure involves dividing the transverse ligament to open the carpal tunnel to relieve pressure and remove thickened synovial tissue. Endoscopic surgery using a fiber-optic camera allows the surgeon to visualize and cut the carpal ligament. This procedure results in faster recovery and minimizes postoperative discomfort and scarring. Though most patients who have carpal tunnel surgery recover completely, recovery can take months.

Perspective and Prospects

The historic roots of carpal tunnel syndrome can be traced back to the 1860s, when meatpackers complained of pain and loss of hand function, which physicians initially attributed to reduced circulation. Modern occupations that require repetitive motions for extended periods—such as typing on a computer keyboard, construction and assembly-line work, and jackhammer operation—have caused a dramatic rise in cumulative trauma disorders such as carpal tunnel syndrome, while other workplace injuries have leveled off.

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