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ElectromyographyDefinitionElectromyography is a test that assesses the health of the muscles and the nerves controlling the muscles. Alternative NamesEMG; MyogramHow the Test is PerformedFor an EMG, a needle electrode is inserted through the skin into the muscle. The electrical activity detected by this electrode is displayed on an oscilloscope, 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 presence, size, and shape of the wave form -- the action potential -- produced on the oscilloscope provide information about the ability of the muscle to respond when the nerves are stimulated. A nerve conduction velocity test is usually performed in conjunction with an EMG. How to Prepare for the TestNo special preparation is usually necessary. Avoid using any creams or lotions on the day of the test. How the Test Will FeelYou may feel some pain or discomfort when the electrodes are inserted, but most people are able to complete the test without significant difficulty. Afterward, the muscle may feel tender or bruised for a few days. Why the Test is PerformedEMG is most often used when people have symptoms of weakness and examination shows impaired muscle strength. It can help to differentiate primary muscle conditions from muscle weakness caused by neurologic disorders. Normal ResultsMuscle tissue is normally electrically silent at rest. Once the insertion activity (caused by the trauma of needle insertion) quiets down, there should be no action potential on the oscilloscope. When the muscle is voluntarily contracted, action potentials begin to appear. As contraction is increased, more and more muscle fibers produce action potentials until a disorderly group of action potentials of varying rates and amplitudes (complete recruitment and interference pattern) appears with full contraction. What Abnormal Results MeanDisorders or conditions that cause abnormal results include the following:
Risks
ConsiderationsTrauma to the muscle from EMG may cause false results on blood tests (such as creatine kinase), a muscle biopsy, or other tests.
Review Date:
9/26/2006 Reviewed By: Kenneth Gross, M.D., Neurology, North Miami, FL. Review provided by VeriMed Healthcare Network. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997-
A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.  |
