Carpal tunnel syndrome: There's light at the end of the tunnel

When nerves travel from the spinal cord to the limbs, they are housed within passageways or tunnels, which may become narrowed for a variety of reasons. When that happens, it puts pressure on the nerve passing through, causing symptoms such as weakness, tingling, or numbness. The best known and most common of these trapped or pinched nerve problems is carpal tunnel syndrome, which affects the median nerve as it passes through the wrist on its way to the thumb, index, and middle fingers (see illustration).

What is it?

The carpal tunnel consists of a U-shaped cluster of eight bones at the base of the palm. A strong ligament, the transverse carpal ligament, arches across the bones, forming the roof of the tunnel. Within the tunnel lies the median nerve, which controls sensation in the palm side of the thumb, the index and middle fingers, and half of the ring finger. It also transmits the impulses to certain hand muscles that allow the fingers and thumb to move. If the carpal tunnel narrows, the resulting pressure decreases the blood supply to the nerves, causing carpal tunnel syndrome.

The classic symptoms are pain, weakness, and tingling in the thumb, index finger, middle finger, and half the ring finger. Often, these symptoms occur at night and awaken you from sleep. Sleeping with the wrists flexed — a common habit — can contribute to the nighttime symptoms. After you awaken, you may need to shake your hand to restore normal feeling. Some people say their hands feel swollen and useless, even though their hands don’t appear swollen. As the condition progresses, you may start to feel tingling during the day, and the pain radiates up to your arm. It may become difficult to make a tight fist, grasp small objects, or do other things with your hands. In severe, chronic cases, the muscles at the base of the thumb weaken. You may even lose the ability to distinguish between hot and cold by touch.

Who gets it?

Carpal tunnel syndrome affects between two percent and three percent of the general population. Women are at least twice as likely to have carpal tunnel syndrome as men, and the risk increases with age. It’s thought to arise from a combination of factors that increase pressure on the median nerve and surrounding tendons. These include the following:

• Heredity. Experts estimate that genes account for about half of cases, based in part on studies that show a much higher risk in women who have an identical twin with the disorder compared to those with a non-identical twin.

• Tunnel size. Although the size of your wrist doesn’t seem to matter, having a smaller carpal tunnel may make you more prone to the problem.

• Diseases. Metabolic diseases (such as diabetes and thyroid disease) and autoimmune diseases (such as rheumatoid arthritis, lupus, and connective tissue disorders) have been linked to a higher risk of developing carpal tunnel syndrome.

• Previous bone dislocation or fracture. These injuries may cause bones to protrude into the carpal tunnel, narrowing it.

• Hormone status. Between 20 percent and 60 percent of pregnant women develop carpal tunnel syndrome, most likely because of fluid retention. Symptoms usually disappear gradually after the baby is delivered but linger for at least a year in many women. Having your ovaries removed (surgical menopause) also appears to increase the risk.

• Body weight. Being overweight or obese appears to raise the risk — perhaps twofold, according to several studies.

• Wrist position. Keeping your wrists bent while sleeping, reading, or driving may contribute to carpal tunnel syndrome.

• Occupation. Carpal tunnel syndrome is more common in people who do assembly-line work — for instance, in industries such as manufacturing, sewing, cleaning, and meatpacking. But despite widespread belief, using a computer — even up to seven hours a day — does not appear to increase the risk for carpal tunnel syndrome.

Diagnosing Carpal Tunnel Syndrome

Your doctor will ask you to describe your symptoms and to recall when, how often, and how severe they are. He/she will examine your hands, arms, shoulders, and neck to determine whether the complaints might be related to daily activities and rule out other conditions that might mimic carpal tunnel syndrome. The doctor will also examine your wrists and hands for signs of tenderness and swelling, and test the sensation in each finger. He/she will also assess the muscles at the base of your hand to see if they show signs of atrophy or weakness.

Doctors also use specific tests to try to elicit the symptoms of carpal tunnel syndrome. In the Tinel’s test, the doctor taps or presses on the median nerve. If that causes tingling in the fingers or a shock-like sensation, the test is positive, meaning you may have carpal tunnel syndrome. The modified Phalen, or wrist-flexion test, involves holding the elbow straight and flexing the hands and wrists. This test is positive if your fingers tingle or feel numb after one minute.

The gold standard test for carpal tunnel syndrome is called electromyography (EMG). It consists of two parts. The first one is a nerve conduction test (also called a nerve conduction velocity or NCV test), which uses a machine that administers mild electric stimulus to the median nerve via small electrodes placed on the hand and wrist. The electrodes measure how quickly the nerves are able to transmit impulses. In the second part, the electromyographer inserts into the muscle a very fine needle that measures the electrical activity of the muscles, which can reveal any possible damage to the median nerve. The EMG not only can tell you the diagnosis of carpal tunnel syndrome, but the exact location of the nerve block, severity of damage, and the prognosis of your condition.

Treating Carpal Tunnel

If you have underlying health problems that may be contributing to carpal tunnel syndrome, such as diabetes or arthritis, they should be treated first.

• Self-help. It’s important to rest the affected hand for at least two weeks, avoiding any activities that may worsen symptoms. In particular, avoid prolonged periods of gripping and pinching. Because holding the wrist down or up can exacerbate symptoms, it can help to wear a splint that keeps your wrist in neutral position. Many people find that wearing a splint at night is an effective treatment. Some hand exercises may be helpful for people with carpal tunnel syndrome, but it’s best to consult a physiatrist (a specialist in physical medicine and rehabilitation) or a physical or occupational therapist for specific exercise recommendations, as improper exercising may worsen the problem.

• Medications. There’s no evidence that ordinary NSAIDs such as aspirin, ibuprofen, and naproxen are effective for treating carpal tunnel syndrome. The same goes for COX-2 medications, such as celecoxib (Celebrex). However, if the cause is enlargement of the tendons inside the canal due to an inflammatory process, then this type of medications may help. On certain patients with more severe involvement, some doctors may prescribe corticosteroid pills, but these should be taken for a limited time and with special precautions for those patients who may be diabetic or hypertensive. There is no scientific evidence of any benefit to the use of high doses of vitamin B6 in this condition. Acupuncture may be helpful, either as an addition or an alternative to other therapies.

• Injections. Corticosteroid injections into the carpal tunnel may relieve symptoms, especially in younger patients who have had symptoms only for a short time. In one study, 70 percent of people with carpal tunnel syndrome who received injections reported being satisfied with the treatment after two weeks, compared with 34 percent who received a placebo. Studies on the long-term benefits of steroid injections have had mixed results, with some finding that for most people, pain returns within two to four months.

• Surgery. Most people improve with one or more of the above treatments, and less than a third end up needing surgery. If you have persistent numbness and pain, and have trouble gripping or grasping things, surgery may be the right choice for you. The goal of surgery is to create more space in the tunnel by releasing the transverse carpal ligament, which relieves pressure on the median nerve. Some procedures are done using local anesthesia and don’t require an overnight hospital stay. New minimally invasive approaches — such as endoscopic and “mini-open” techniques — leave only a very small scar. Success rates for surgery are high, with 80 percent to 90 percent of people reporting relief of daytime and nighttime symptoms after six weeks.