Carpal Tunnel Syndrome - Diagnosis

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• 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), and those on the second or third fingers.

Nerve conduction 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.

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