EMG/NCV: The Value of Physiologic Testing

By | May 26, 2015

A NCV test of the median nerve in the area of the carpal tunnel.

A NCV test of the median nerve in the area of the carpal tunnel.

Margie was seen by Marty Levine a very good neurologist and electrophysiologist in Encino. To my surprise and from rereading his report to Marty’s surprise as well the test showed minimal radicular abnormalities and severe slowing of conduction in the distal median nerve in the area of the carpal tunnel. An electromyogram and nerve conduction velocity test is a physiological test wherein several electrodes are placed in the area of the spine and the extremity of interest. A small stimulating electrical current is applied the most proximal electrode (the electrode closest to the spine) and the electrical activity in the nerve and muscle distally (downstream, father from the spine) is measured.  By analyzing the shape of the electrical impulse as well as the time that it takes to get to the recording electrode, the function of the nerve can be assessed. In general the sharper the spike and the sooner that it arrives at the recording electrode the healthier the nerve is. By placing electrodes in proximity to different nerves, roots and trunks you can attempt to isolate which is most affected. Likewise by inserting several stimulating and recording electrodes along the length of a single nerve you can infer where along the course of the nerve the pathological process is causing the damage. In Margie’s case it turned out that none of the anatomical abnormalities seen on the MRI of her cervical spine were causing the problem but a constricting band in the area of the wrist appeared to be the problem. At Schlesinger Pain Centers it is our practice to obtain a physiologic test such as an EMG/NCV in all cases where the diagnosis remains unclear after standard history, physical exam and anatomical testing.

Sensory NCS: An example screenshot showing the results of a sensory nerve conduction velocity study of the right median nerve.

Sensory NCS: An example screenshot showing the results of a sensory nerve conduction velocity study of the right median nerve.


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