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What nerve tests are used to diagnose carpal tunnel syndrome?

Dr. Prosper A. Benhaim, MD
Orthopedic Surgeon

To diagnose carpal tunnel syndrome, the most common nerve test that is performed is a nerve conduction study (NCS) or electromyogram (EMG). This study involves stimulating the nerve at the forearm or wrist level, and testing the response at the finger level. Testing the response over sensory nerves provides information about how well the sensory component of the nerve is working. Testing the response over a muscle that is supplied by the nerve provides information as to how well the motor component of the nerve is working. In the typical carpal tunnel syndrome, people will have sensory changes evident on the NCS much earlier than motor changes. Most people with carpal tunnel syndrome will have a positive NCS or EMG. Some people, however, will have typical carpal tunnel syndrome symptoms, but still have a negative NCS. In those people, a diagnostic cortisone injection can be helpful. More recently, both MRI and ultrasound have been suggested as alternative diagnostic tests, based on the fact that the median nerve will typically have a larger cross-sectional area in people with carpal tunnel syndrome than in those without. Although MRI and ultrasound are sometimes useful, the gold standard for diagnosis is still considered to be the NCS or EMG.

Two tests commonly used to diagnose carpal tunnel syndrome are electromyography (EMG) and nerve conduction studies. In electromyography, tiny needles are put into the muscles in your hand to measure the electric activity when your muscles are contracted and when they are at rest. In nerve conduction studies, electrodes pass a current through a particular nerve and the time it takes for the current to reach the muscle is measured. Both tests can show if any nerves or muscles have been damaged.

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