Carpal Tunnel Syndrome

Description

Alternative Names

Diagnosis

Carpal tunnel syndrome (CTS) is most accurately diagnosed using the patients' descriptions of symptoms plus electrodiagnostic tests that measure nerve conduction through the hand. If electrodiagnostic testing is not available, then symptom descriptions and a series of physical tests are useful.

Diagnosing CTS, however, is not straightforward. Only a small fraction of patients exhibit all three factors necessary for a clear diagnosis:

• Classic CTS symptoms.
• Specific physical findings.
• Abnormal electrodiagnostic test results.

Many people have abnormal electrodiagnostic test results but have no classic symptoms or even no symptoms at all. Furthermore, about 15% of the population has symptoms consistent with CTS, but most do not show test results indicating the disorder. In fact, in a 2001 study, some patients who had symptoms but whose nerve and physical tests are normal still experienced relief after CTS surgery.

Symptom Description and Severity

Many cases of CTS are a combination of a medical problem exacerbated by repetitive stress factors at work. The patient should give the physician a detailed history and description of any complaints, in any part of the body. The patient should report in detail any daily activities that require repetitive hand or wrist actions, abnormal postures, or other chronic situations that could affect the nerves in the neck, shoulders, and hands. The patient should report whether the symptoms especially appear at night or after particular tasks.

Questionnaires. The use of specific questionnaires that score results are quite accurate in assessing the severity of the condition.

Hand Diagram. A diagram of the hand and wrist, usually divided into six regions, is a very useful diagnostic tool. Patients are asked to indicate where their symptoms, including pain, numbness, or tingling are by locating the affected areas on the diagram. They may also be asked to rate the severity of their symptoms. A diagnosis is probable if at least two of fingers 1, 2, or 3 have these symptoms and if there is pain in or near the wrist. CTS is possible if at least one of these fingers has symptoms. It is unlikely if there are no symptoms in these fingers, the palm, or the wrist.

Ruling Out Underlying Medical Disorders

One of the most important first steps in diagnosing CTS is to rule out any underlying medical disorders that may be contributing to the condition. Experts emphasize the need to fully examine patients presenting with symptoms of CTS. Relying only on CTS symptoms and personal or work histories may result in the failure to detect (and thus properly treat) underlying medical conditions that could be serious. If the doctor suspects that an underlying medical condition may be exacerbating the symptoms, laboratory tests will be performed. The doctor may take an x-ray, for example, to check for arthritis or fractured bones.

Raynaud's Phenomenon. Raynaud's phenomenon produces symptoms of numbness and tingling or pain in the fingers of one or both hands. It is usually brought on by cold or stress and is treated with warmth or, in severe cases, medications that may open blood vessels. People with this disorder, in fact, appear to be at higher risk for carpal tunnel syndrome and there may be some associations between the two conditions.

Arthritic Conditions. Arthritic conditions, including rheumatoid arthritis, gout, and osteoarthritis, can all cause pain in the hands and fingers that may mimic but not actually be treatable as carpal tunnel disease.

Muscle and Nerve Diseases. Any disease or abnormality that affects the muscles and nerves, including those in the spine, may produce symptoms in the hand that mimic carpal tunnel.

Ruling Out Other Cumulative Trauma Disorders

About 25% of patients with suspected work-related cumulative trauma or repetitive stress disorders have evidence of other conditions that resemble, but are not, carpal tunnel syndrome. A definitive diagnosis is often difficult. Most require treatments similar to those used for CTS: rest, immobilization, steroid injections, and even surgery if conservative management is unsuccessful.

Physical Self-Assessment Tests for Carpal Tunnel Syndrome

The following findings are helpful in identifying carpal tunnel syndrome:

• Less sensitivity to pain where the median nerve runs through to the fingers.
• Thumb weakness.
• Inability to tell the difference between one and two sharp points on the fingertips. (This is a late sign of carpal tunnel.)

Flick Signal. One important and simple test of carpal tunnel is the "flick" signal:

• The patient is asked, "What do you do when your symptoms are worse?"
• If the patient responds with a motion that resembles shaking a thermometer, then the physician can strongly suspect carpal tunnel.

Testing for Thumb Weakness. Two questions are useful in determining thumb weakness:

• Can the thumb rise up from the plane of the palm?
• Can the thumb stretch so that its pad rests on the pad of the little finger pad?

Provocation Tests. Certain tests are conducted to produce symptoms:

• Phalen's Test. In Phalen's test, the patient rests the elbows on a table and lets the wrists dangle with fingers pointing down and the backs of the hands pressed together (like backward praying). If symptoms develop within a minute, CTS is indicated. (If the test lasts for more than a minute even patients without CTS may develop symptoms.) This test may be particularly important in determining the severity of CTS and assessing the results of treatment.
• Tinel's Sign. In the Tinel's sign test, the physician taps over the median nerve to produce a tingling or mild shock-sensation.
• Pressure Provocation Test. The physician presses over carpal tunnel for 30 seconds to produce tingling or shock in the median nerve.
• Tourniquet Test. This test employs an inflatable cuff that applies pressure over the median nerve to produce tingling or small shocks.

Electrodiagnostic Tests

Electrodiagnostic tests that analyze the electric waveforms of nerves and muscles to detect median nerve compression in the carpal tunnel are the best methods for confirming a diagnosis of CTS at this time. Physicians who perform these tests should be certified by the American Board of Electrodiagnostic Medicine, which uses rigorous standards in qualifying doctors.

Specific electrodiagnostic tests called nerve conduction studies and electromyography are the most common ones performed:

• Nerve Conduction Studies. To perform nerve conduction studies, surface electrodes are first fastened to the hand and wrist. Small electric shocks are then applied to the nerves in the fingers, wrist, and forearm to measure the speed of conduction of sensory and motor nerve fibers. In suspected cases of CTS, nerve conduction tests can identify over 85% of true carpal tunnel syndrome cases and eliminate 95% of those that are not true CTS. They are less accurate in identifying mild CTS, however. Patients should be sure their practitioners perform tests that compare a number of internal responses--not just routine testing that records only the responses of thenar muscles (located in the palm at the base of the thumb) and second or third fingers. These tests can also detect causes of symptoms that mimic CTS but should be attributed to other problems, such as pinched nerves in the neck or elbow or thoracic outlet syndrome.
• Electromyography. To perform electromyography, a fine, sterile, wire electrode is inserted briefly into a muscle and the electrical activity is displayed on a viewing screen. Electromyography can be quite painful and is less accurate than nerve conduction. Some experts question, in fact, whether it adds any valuable diagnostic information. They suggest it be limited to unusual cases or when other tests indicate that the condition is aggressive and may increase the risk for rapid, significant injury.

Limitations. Electrodiagnostic studies are not well standardized, and certain conditions can skew the results of either test:

• Obesity can slow the speed of electrical conduction.
• Anxiety can slow the speed.
• Women and the elderly normally have slower conduction times than younger adult men.
• Temperature also affects nerve conduction speed. Room temperature should be strictly controlled and physicians should take into consideration any climatic conditions that might affect outcome.

Ruling out other causes is extremely important in order to avoid unnecessary surgery for CTS. Modifications and improvements of these tests are continually being made.

Note: People with abnormal results but who have no CTS symptoms are at no higher risk for CTS than those with normal results and no symptoms.

A diagnosis of carpal tunnel syndrome may follow testing the affected hand for numbness, tingling, weakness and/or pain in specific areas. Muscle and nerve conduction tests may also help affirm or rule out carpal tunnel syndrome.

Imaging Techniques

Ultrasound. Ultrasound imaging, a relatively inexpensive technique that uses sound waves, is showing promise. Studies indicate that it can identify up to 85% of CTS cases, and some suggest it is as effective as electrodiagnostic tests. It may be effective for ruling out other causes of hand pain, such as tendon injuries, tenosynovitis (swelling of the tendon lining), cysts, and blood clots in the median artery (a rare complication that can cause the sudden onset of CTS symptoms). However, results are mixed on its accuracy. Newer color Doppler ultrasound and other technological advances are improving the results achieved with this technique.

MRI. Magnetic resonance imaging (MRI), an advanced imaging technique, is being adapted to distinguish weak nerve signals from surrounding tissue, so that eventually it may be able to precisely diagnose CTS. However, studies in 2002 note that it requires special expertise, has limited diagnostic accuracy, and is still too expensive at present for routine use. Currently, MRI is accurate in diagnosing carpal tunnel syndrome about 80% of the time, compared to about 85% using electrodiagnostic tests, which remains the gold standard. MRI may be most effective for detecting any internal injuries, tumors, or arthritis or joint damage that might be causing the problem. It may also be valuable in selecting surgical candidates when electrodiagnostic tests produce unusual results or indicate more severe disease than expected or for evaluating patients if surgery fails to bring relief.