What is the role of electromyography (EMG) testing in electrodiagnosis?

Updated: Jan 27, 2020
  • Author: Adam B Agranoff, MD; Chief Editor: Stephen Kishner, MD, MHA  more...
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EMG was the first electrodiagnostic test to be developed. This procedure involves the placement of a needle into various muscles to record different stages of muscle activity, including rest, minimal contraction, and maximal activity. At rest, normal muscle is electrically silent. Damaged muscle tissue may result in spontaneous depolarization of individual muscle fibers. This abnormal activity can be detected during the needle examination portion of the electrodiagnostic examination.

Primary nerve injuries that are severe enough to create neurotmetic or axonotmetic lesions, which result in Wallerian degeneration of the nerve, demonstrate fibrillation and positive sharp-wave discharges at rest. Fibrillations and positive sharp waves are pathognomonic for nerve injuries. Primary muscle disorders can also be detected by EMG.

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