Abstracts

Computer-aided analysis of EEG frequency content has been used in long-term epilepsy monitoring to identify possibly relevant epochs in long files, to help define the time of seizure-onset or to highlight significant frequency peaks in artifact-contaminated seizures. We aim to evaluate the contribution of EEG frequency analysis for the lateralization of seizure onset in patients with temporal lobe epilepsy considered for resective epilepsy surgery., We reviewed the EEG data base of the epilepsy monitoring unit of the university of Munich and included seizures of 31 consecutive patients with temporal lobe epilepsy considered for resective epilepsy surgery. The ictal EEGs were first analysed conventionally by standard expert visual analysis. In a second step the ictal EEG files were processed using the Density Spectral Array (DSA) tool of BESA (Megis Co.) program, producing a color-coded display window where right and left hemispheric channel information are separated. This display was reviewed by a person blinded to clinical, radiological and conventional EEG data, who aimed to identify, for each seizure, any graphic patterns suggestive of an ictal frequency shift., Patients were predominantely female (n=22), with ages between 8 and 58 years (average 38 years); epilepsy etiology was hippocampal sclerosis (n=20), cavernoma (n=2), low-grade tumor (n= 2), malformation of cortical development (n=1), dual pathology (sequelae of viral encephalitis plus hippocampal sclerosis, n=1) and unknown (n=4). 139 ictal EEGs were reviewed, averaging 4,5 seizures per patient (minimum 1, maximum 8). Recognizable frequency shifts ([quot]chirps[quot]) allowing clear lateralization of seizures were found at seizure onset in 74,2% (23 of 31) of the patients and in 49,6% (69 of 139) of the seizures. Visual estimate of seizure frequency at onset was in the range of 5-10 Hz, with a tendency to decrease as seizures evolved in time. Conventional EEG showed a regional EEG seizure pattern in all of these patients. The lateralization using DSA was correct in all but one patient in whom the frequency chirp occured late (20 seconds post-onset) in the seizure evolution., The analysis of frequency spectra at seizure onset in temporal lobe epilepsy provides lateralizing information in aproximately 50% of the seizures and in 75% of the patients considered for temporal lobectomy. Further studies should evaluate the diagnostic yield of the method prospectively., (Supported by Portuguese League Against Epilepsy.)