Analysis of Generalized Interictal Discharges Using Dipole Source Imaging (P04.014)

Objective: The objective of this study was to investigate focal spatiotemporal characteristics of the scalp interictal generalized spike and wave (GSW) discharges in patients with idiopathic generalized epilepsies (IGE) using quantitative electroencephalogram (qEEG). Background Investigations have shown that patients with IGE have mild focalities. These focal abnormalities probably are related with IGE mechanisms which involves the thalamo-cortical circuitry. Experimental investigations points to a focal onset of the GSW discharges in models of absence seizure. qEEG analysis may be able to detect subtle focalities in these patients. Design/Methods: 21 patients (8 woman, mean age 29±12 years) with IGE were investigated. Subjects underwent routine EEG which was performed with a 19-channel recorder, 20 minutes duration, 10-20 system of electrode placement, photic stimulation and hyperventilation. EEGLAB software was used for EEG processing and analysis. All GSW discharges were entirely selected and stored. Discharges were submitted to decomposition into temporally independent and spatially fixed components by independent component analysis. For dipole fitting a spherical four-shell head model and nonlinear adjustment were used. A single equivalent dipole source model was calculated for each component. To identify common patterns of discharge propagation cluster analysis of the equivalent dipole obtained for each component was used. Closely located dipole sources were classified into same subsets (clusters). Results: 207 discharges (mean 10±16 per patient, range 1-73) were evaluated. In 14 patients (81%) source analysis showed the main independent component cluster (ICC) centroid localized in the cingulate gyrus. In 5 patients ICC centroid was localized in basal ganglia and in 2 patients ICC centroid was in the frontal lobe (orbital and middle frontal gyrus). Conclusions: There is not a common source for the GSW discharges in patients with IGE. However, it was disclosed a clear-cut focal predominance in the cingulate gyrus and frontal regions. Supported by: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP). Disclosure: Dr. Betting has nothing to disclose. Dr. Blasque has nothing to disclose. Dr. Pereira has nothing to disclose. Dr. Fonseca has nothing to disclose. Dr. Betting has nothing to disclose.