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Electromyography

Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.

How the Test is Performed

The health care provider inserts a very thin needle electrode through the skin into the muscle. The electrode on the needle picks up the electrical activity given off by your muscles. This activity appears on a nearby monitor, and may be heard through a speaker.

After placement of the electrodes, you may be asked to contract the muscle. For example, by bending your arm. The electrical activity seen on the monitor provides information about your muscle's ability to respond when the nerves to your muscles are stimulated.

A nerve conduction velocity test is almost always performed during the same visit as an EMG.

How to Prepare for the Test

No special preparation is usually necessary. Avoid using any creams or lotions on the day of the test.

Body temperature can affect the results of this test. If it is extremely cold outside, you may be told to wait in a warm room for a while before the test is performed.

If you are taking blood thinners or anticoagulants, inform the provider performing the test before it is done.

How the Test will Feel

You may feel some pain or discomfort when the needles are inserted. But most people are able to complete the test without problems.

Afterward, the muscle may feel tender or bruised for a few days.

Why the Test is Performed

EMG is most often used when a person has symptoms of weakness, pain, or abnormal sensation. It can help tell the difference between muscle weakness caused by the injury of a nerve attached to a muscle, and weakness due to nervous system disorders, such as muscle diseases.

Normal Results

There is normally very little electrical activity in a muscle while at rest. Inserting the needles can cause some electrical activity, but once the muscles quiet down, there should be little electrical activity detected.

When you flex a muscle, activity begins to appear. As you contract your muscle more, the electrical activity increases and a pattern can be seen. This pattern helps your doctor determine if the muscle is responding as it should.

What Abnormal Results Mean

An EMG can detect problems with your muscles during rest or activity. Disorders or conditions that cause abnormal results include the following:

Risks

Risks of this test include:

  • Bleeding (minimal)
  • Infection at the electrode sites (rare)

Alternative Names

EMG; Myogram; Electromyogram

References

Chernecky CC, Berger BJ. Electromyography (EMG) and nerve conduction studies (electromyelogram)-diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:468-469.

Katirji B. Clinical electromyography. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier; 2016:chap 35.

Review Date 5/30/2016

Updated by: Amit M. Shelat, DO, FACP, Attending Neurologist and Assistant Professor of Clinical Neurology, SUNY Stony Brook, School of Medicine, Stony Brook, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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