Electromyogram (EMG) and Nerve Conduction Studies

EMG (Electromyography), Nerve Conduction Studies

How It Is Done

An electromyogram (EMG) is done in a hospital, clinic, or doctor's office. A special room that stops any outside electrical interference may be used. The test may be done by an EMG technologist or a doctor specializing in diseases of the nervous system (neurologist) or in physical rehabilitation (physiatrist).

You will be asked to lie on a table or bed or sit in a reclining chair so your muscles are relaxed.

Electromyogram

The skin over the areas to be tested is cleaned with a special soap. A needle electrode that is attached by wires to a recording machine is inserted into a specific muscle.

Once the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. Then the technologist or doctor asks you to tighten (contract) the muscle slowly and steadily. This electrical activity is recorded.

The electrode may be moved a number of times to record the activity in different areas of the muscle or in different muscles.

The electrical activity in the muscle is shown as wavy and spiky lines on a special video monitor (oscilloscope) and may also be heard on a loudspeaker as machine gun-like popping sounds when you contract the muscle. The activity may also be recorded on video.

An EMG may take 30 to 60 minutes. When the testing is done, the electrodes are removed and those areas of the skin where a needle was inserted are cleaned. You may be given pain medicine if any of the test areas are sore.

Nerve conduction studies

In this test, several flat metal disc electrodes are attached to your skin with tape or a special paste. A shock-emitting electrode is placed directly over the nerve and a recording electrode is placed over the muscles under control of that nerve. Several quick electrical pulses are given to the nerve, and the time it takes for the muscle to contract in response to the electrical pulse is recorded. The speed of the response is called the conduction velocity.

The same nerves on the other side of the body may be studied for comparison. When the test is completed, the electrodes are removed.

Nerve conduction studies are done before an EMG if both tests are being done. Nerve conduction tests may take from 15 minutes to 1 hour or more, depending on how many nerves and muscles are studied.

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Author:	Monica Rhodes	Last Updated: July 29, 2008
Medical Review:	Anne C. Poinier, MD - Internal Medicine Colin Chalk, MD, CM, FRCPC - Neurology
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