What is Electrodiagnostic Medicine?

The electrodiagnostic medicine consultation is a direct extension of the neurologic portion of the physical examination. The examination can be helpful in evaluating the causes of numbness, tingling, pain, weakness, fatigue, and muscle cramping. Several types of tests are used to study nerve and muscle function. These include nerve conduction studies (NCSs), needle clectromyography (EMG), and evoked potentials.

An electrodiagnostic medicine consultant undergoes special training in electrodiagnostic medicine procedures. The knowledge and expertise gained from such specialized medical training maximizes the ability of the consultant to consider appropriate differential diagnoses in planning and performing the electrodiagnostic examination. The expertise enables the consultant to assist referring physicians in establishing diagnoses, determining prognoses, and assisting in proper management.

The examination usually takes 20 to 60 minutes. There are no restrictions on activity before or after the testing and there are no lasting aftereffects.

NCSs and evoked potentials should be performed by a physician or a trained technologist under the direct supervision of a physician. The needle EMG examination should be performed by a physician with special training in this area.

Nerve Conduction Studies

NCSs test how well signals travel along a nerve and can help find the cause of abnormal nerve function. Signals arc made to travel along the nerve by applying small electric pulses to the nerve at one site and recording the response at a different place along the nerve. The small electric pulses cause a short, mild tingling feeling. The nerve's response is picked up by a recording instrument and then is measured by the physician or technologist performing the test. Several nerves may need to he tested depending on the type of problem.

Needle Examination (EMG or electromyogram)

During the needle EMG portion of the examination, the physician inserts a small needle into a muscle to record the electrical activity of the muscle. The electrical activity of the muscle is fed into the recording instrument and the physician then analyzes it by looking at a signal on the scope and listening to the sounds the activity makes through the speaker. This test can help determine if there are abnormalities in the muscle or the nerve going to it.

There may be mild discomfort when the needle is inserted into the muscle. The needles are discarded after use or sterilized before being used on another patient to prevent the transmission of infections.

Evoked Potentials

Evoked potentials evaluate the function of nerve pathways that carry signals through the spinal cord, vision pathways, and hearing pathways. Nerve signals are produced in these nerves by applying small electric pulses to the nerves of the legs or arms, by pulses of light to the eyes, or by clicks of sound to the ears. The nerve's response is picked up from the skin over the surface of the spinal cord or the head.

Special Precautions

You should inform the physician prior to the examination if you are on blood thinners or have hemophilia. The physician should also be informed if you have a cardiac pacemaker or use a transcutaneous electrical nerve stimulator (TENS) unit. Avoid using skin lotions the day of the test. If you have myasthenia gravis you should ask your physician whether or not to take medications, such as Mestinon, before the examination.

Results

When the examination is completed, the electrodiagnostic medicine consultant will analyze the results and report them to the physician who referred you for the tests. Your referring physician will use the test results to help decide on proper management.