Positive Interictal Epileptiform Discharges in Adults: a Case Series of a Rare Phenomenon

The polarity of interictal epileptiform discharges (IEDs) recorded from scalp EEG is predominantly negative relative to a suitable reference electrode and is generally interpreted as indicative of dipoles oriented perpendicularly to the cortical surface with their negative poles near the surface (Gloor, 1985). The deeper positive poles usually fail to produce a detectable surface potential but can be recorded with invasive electrodes. In some instances, horizontal dipoles such as benign epileptiform discharges of childhood can be recorded from the scalp surface showing both, the positive and the negative potential particularly with generators in the central or Sylvian fissure (Lüders et al., 1987).

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