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Test: Nerve and Muscle Electrical Tests

Nerve and muscle electrical tests consist of nerve conduction studies and electromyography (EMG). Nerve conduction studies are used to assess how well a nerve is conducting electrical impulses. They are often followed by EMG to see whether symptoms, such as weakness, are due to a disorder of the muscle or the nerve supplying it. Both tests are usually done on an outpatient basis. Each takes about 15 minutes and may cause some discomfort.

Nerve conduction studies

Nerve conduction studies are carried out to assess nerve damage in disorders such as peripheral neuropathies. A nerve is stimulated by an electrical impulse, and the response to the stimulus and the speed at which this response travels along the nerve indicates whether the nerve is damaged and the nature and extent of the damage.

During the procedure

A probe is held against the skin to stimulate the nerve to be tested. The signal that is produced by the nerve is picked up by a recording electrode placed further along the nerve on the skin.

Results

Nerve conduction trace

This trace shows a normal electrical impulse through a nerve. The nerve is stimulated, and the speed at which the impulse travels through the nerve is measured.

Electromyography

EMG is used to differentiate between nerve and muscle disorders and to diagnose disorders such as muscular dystrophy. A fine needle is used to record the electrical activity of a muscle at rest and when contracting. The results are recorded on a trace.

During the procedure

A needle placed in or on the muscle records electrical activity at rest and when you contract the muscle. A ground electrode eliminates background electrical activity.

Results

EMG trace

This trace shows normal patterns of electrical activity in a muscle at rest and when contracting.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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