Electromyography

EMG; Myogram; Electromyogram

Definition

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

How the Test is Performed

Your health care provider inserts a very thin needle electrode through your skin into one of your muscles. 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. The velocity test is done to see how fast and strong electrical signals move through a nerve.

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 a muscle or other nervous system disease.

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 provider 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)

References

Katirji B. Clinical electromyography. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 36.

Preston DC, Shapiro BE. Basic overview of electromyography. In: Preston DC, Shapiro BE, eds. Electromyography and Neuromuscular Disorders. 4th ed. Philadelphia, PA: Elsevier; 2021:chap 12.

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Review Date: 6/13/2024

Reviewed By: Joseph V. Campellone, MD, Department of Neurology, Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.


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