Abstracts

This study was undertaken to test the hypothesis that seizures in generalized epilepsies may have as yet unrecognized focal onsets.
Seven adults (age range 19-40) with idiopathic generalized epilepsy syndromes, as defined by International League Against Epilepsy criteria, were recorded using 256 channel scalp EEG. The ictal onsets (at least three per subject) were analyzed using the BESA source analysis program. Using pattern search, the onset phases were aligned, averaged, and high pass filtered to analyze the intial spike-wave component by multiple source analysis. The onsets were visualized in different source regions using individual source montages created by BESA.
Focal, unilateral mesial frontal onsets were observed in six subjects (right sided onset in five, left-sided in one). The most consistent locations were in the anterior cingulate gyrus or the sulcus above it. Only one subject demontrated bilateral mesial frontal onsets. Side of onset could be identified by orientation and propagation which was most rapid to other regions of ipsilateral frontal lobe, followed by spread to opposite frontal lobe and to temporal regions. Use of different source montages yielded similar onset patterns, while propagation patterns varied.
Our results support emerging concepts from experimental studies that generalized seizures do, indeed, have focal onset zones. Demonstration of such focality requires the application of techniques that provide sufficient spatial sampling and resolution of source localization.