What is abnormal slow activity on EEG of focal lesions?

Updated: Aug 06, 2019
  • Author: Selim R Benbadis, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Abnormal slow activity is by far the most common EEG manifestation of focal brain dysfunction. The abnormality that correlates best with the presence of a structural lesion is polymorphic or arrhythmic (as opposed to monomorphic or rhythmic) delta (ie, 1-3 Hz) slowing. This is all the more reliable when it is continuous, unreactive (ie, characterized by lack of change between states, such as wake or sleep, or in response to external stimuli), of high amplitude, polymorphic, and unilateral. The localization of slow potentials follows the same rules as that of epileptiform discharges. Thus, "phase reversals" are useful to localize slow potentials and do not imply abnormality or epileptogenicity.

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