Carpal Tunnel Syndrome - Diagnosis

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• 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.
• Temperature also affects nerve conduction speed. When undergoing testing, doctors should strictly control room temperature to lessen its impact.

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 who have no CTS symptoms are at no higher risk for CTS than those with normal results and no symptoms.

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. A 2005 study comparing high-resolution ultrasonography with electromyography found that ultrasonography may be helpful for estimating the symptom severity and problems with nerve conduction.

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. MRI is accurate in diagnosing carpal tunnel syndrome about 80% of the time, compared to about 85% using electrodiagnostic tests, which remains 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.

Review Date: 04/01/2006
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital