Diagnosis:

Carpal tunnel syndrome is most accurately diagnosed using the patients' descriptions of symptoms, and electrodiagnostic tests that measure nerve conduction through the hand. If electrodiagnostic testing is not available, 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 without classic symptoms or any symptoms at all. Furthermore, about 15% of the population has symptoms consistent with CTS, but most do not show test results indicating the disorder.

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 doctor 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 regular situations that could affect the nerves in the neck, shoulders, and hands. The patient should also report whether the symptoms are more likely to 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 are, including pain, numbness, or tingling, 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 of CTS, laboratory tests will be performed. The doctor may take an x-ray, for example, to check for arthritis or fractured bones.

Arthritic Conditions. Arthritic conditions, including rheumatoid arthritis, gout, and osteoarthritis, can all cause pain in the hands and fingers that may mimic carpal tunnel disease. The treatment for these conditions, however, is different.

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 syndrome.

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 treatment is unsuccessful.

Physical 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, the doctor 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 can 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. 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 doctor taps over the median nerve to produce a tingling or mild shock-sensation.
• Pressure Provocation Test. The doctor presses over the 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.
• Hand Elevation Test. The patient raises their hand overhead for 2 minutes to produce symptoms of CTS. The test was recently proven to be accurate and may provide useful information when combined with the Tinel's and Phalen's tests.

Electrodiagnostic Tests

Electrodiagnostic tests analyze the electric waves of nerves and muscles. These tests can help detect median nerve compression in the carpal tunnel.

Electrodiagnostic tests are the best methods for confirming a diagnosis of CTS at this time. Doctors 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 tests can also detect causes of symptoms that mimic CTS but are caused by other problems, such as pinched nerves in the neck or elbow, or thoracic outlet syndrome.

• 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 how fast a signal travels through the nerves that control movement and sensation. 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 muscles located in the palm at the base of the thumb. They should also make sure the tests measure responses on the second or third fingers.
• 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.

While electrodiagnostic studies are frequently done to confirm the diagnosis of carpal tunnel syndrome in patients with classic symptoms, they are also performed on patients with symptoms that do not point to carpal tunnel syndrome as clearly. Doctors must interpret test results in these patients more carefully.

Portable electrodiagnostic testing. Portable electronic devices (such as NC-Stat, Neurosentinel, and the Nervepace digital electroneurometer) are being evaluated for measuring nerve conductivity. They are relatively quick and easy to use on a large scale in an industrial facility. However, the Advancing Association of Neuromuscular and Electrodiagnostic Medicine maintains that these devices are experimental and are not effective substitutes for standard electrodiagnostic studies. These devices are not well studied in clinical trials.

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 of electrical conduction.
• Women and the elderly normally have slower conduction times than younger adult men.

A diagnosis of carpal tunnel syndrome may follow testing the affected hand for numbness, tingling, weakness 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 some 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, studies of ultrasound accuracy in CTS diagnosis yield mixed results. In addition, there are no accepted standard diagnostic criteria for carpal tunnel syndrome using ultrasound.

MRI. Magnetic resonance imaging (MRI) has been studied as a tool to evaluate the median nerve. It requires special expertise, has limited diagnostic accuracy, and is still too expensive for routine use. Electrodiagnostic tests remain the preferred method of diagnosis. MRI may be most effective for detecting any internal injuries, tumors, 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. Additionally, an MRI may be useful for evaluating patients if surgery fails to bring relief.