GENERALIZED BACKGROUND QEEG ABNORMALITIES IN LOCALIZED SYMPTOMATIC EPILEPSY

Spectral features of EEG background activity were studied in patients with localized symptomatic epilepsy (LSE), with origin in the frontal or temporal lobes. Z-values of high resolution spectra and measures of the parametric (xi alpha) model of the EEG were obtained for all 10/2 0 System leads and were compared with those obtained in a control grou p. Comparisons were performed between syndromic Variants of LSE and be tween subgroups of patients with or without paroxysmal activity in the ir digital EEGs (dEEG). Marked reduction of the energy in the alpha ra nge and a mild increase in the theta range were found in the patients, unrelated to the syndromic variant of the epilepsy. These deviations from normality were widespread on the scalp and were not related to an tiepileptic medication. Non-parametric testing showed a positive corre lation between the magnitude of the quantitative EEG abnormalities and the amount of paroxysmal activity in the dEEG. Slowing of the mean fr equency of alpha components of the spectra, an actual decrease of powe r in the alpha range and an increase in the theta range explained the results. The most striking finding of this paper is that focal epilept ogenesis may have a generalized impact in the frequency composition of EEG. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.