Carpal Tunnel Syndrome - Diagnosis

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.)

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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 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 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 doctor taps over the median nerve to produce a tingling or mild shock-sensation.
Pressure Provocation Test. The doctor 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.
Hand Elevation Test. The patient raises his or her overhead for 2 minutes to produce symptoms of CTS. It has recently been found to be accurate and may provide useful information when combined with the Tinel's and Phalen's tests.

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. 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 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.
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.