What are EMG artifacts on EEG?

Updated: Oct 09, 2019
  • Author: Selim R Benbadis, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

Answer

Myogenic potentials are the most common artifacts (see images below). Frontalis and temporalis muscles (eg, clenching of jaw muscles) are common causes. Generally, the potentials generated in the muscles are of shorter duration than those generated in the brain and are identified easily on the basis of duration, morphology, and rate of firing (ie, frequency). Particular patterns of electromyogram (EMG) artifacts can occur in some movement disorders. Essential tremor and Parkinson disease can produce rhythmic 4- to 6-Hz sinusoidal artifacts that may mimic cerebral activity.

Another disorder that can produce repetitive muscle artifacts is hemifacial spasm. The photomyoclonic response is a special type of EMG artifact that occurs during intermittent photic stimulation. Some subjects contract the frontalis and orbicularis muscles. These contractions occur approximately 50-60 milliseconds after each flash, disappear after eye opening and use of paralyzers, are located mostly frontally, and have no concomitant EEG changes.

Electromyogram (muscle) artifact best observed in Electromyogram (muscle) artifact best observed in the left temporal region. ECG artifact also is present, best observed in the posterior region.
Electromyogram (muscle) artifact. These waveforms Electromyogram (muscle) artifact. These waveforms represent motor unit potentials as typically observed on needle electrode examination during electromyogram, with a frequency of 20-100 Hz. Distribution varies, and in this case it is more prominent on the left side. Such artifact can be diminished by the judicious use of the high-frequency filter. (This sample has the default setting of high-frequency filter 70 Hz.)

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