Asymmetry in delta activity in patients with focal epilepsy

The localization of epileptogenic foci usually relies on multiple factors. The validity of background EEG abnormalities in lateralizing or localizing the focus was examined. Asymmetries in delta activity were measured by comparing EEGs of epileptic subjects to that of control subjects. The relationships of MRI, CT and pathological findings with delta asymmetries were also noted. In only 2 of 22 patients, delta activity showed no asymmetry. In 17 patients, delta asymmetries correlated with the side of the focus, and in the remaining 3 patients, predominant delta activity was observed in the hemisphere contralateral to the focus. The analysis of the relationship between delta activity and lesions observed on the CT scan was inconclusive. The area exhibiting predominant delta activity frequently coincided with the regions showing solitary discrete lesions on MRI scans. The results suggest that slow wave abnormalities, when measured by comparison to a control population, can be useful in lateralizing the epileptogenic focus.