Normal Variants and Unusual EEG Patterns

This chapter deals with a group of electroencephalographic waveforms that can occur in normal population. Even if they sometimes mimic pathological waves, these waveforms are not related to epilepsy or other neurologic conditions. They can be divided into two groups: normal variants and unusual benign epileptiform patterns. Normal variants consist of non-pathological variants of the background rhythm usually seen in the occipital (slow physiological posterior activities) or centroparietal areas (mu rhythm). Benign epileptiform patterns are unusual waveforms that bear some resemblance to epileptiform activity, but they have no established relationship with epilepsy. The differential diagnosis between normal elements, abnormal elements, and artifacts is challenging even for expert neurophysiologists. To avoid mistakes and misinterpretations, some simple practical rules are proposed at the end of the chapter.