Validation of Criteria for Identification of Epileptiform Discharges in EEG Recordings of Patients With Epilepsy

Electroencephalography (EEG) records electric activity of the brain using electrodes placed on the scalp. EEG is an important tool in the diagnostic work-up of patients with epilepsy. Specific types of sharp EEG discharges (epileptiform discharges) are associated with patients with epilepsy. The International Federation of Clinical Neurophysiology (IFCN) has recently published a set of six operational criteria for identifying epileptiform discharges. At least four criteria need to be present in order to classify a discharge as epileptiform. These criteria are largely based on expert opinion and have not been validated yet. It is not clear what the sensitivity and specificity of these criteria are, and which combination of these criteria are optimal. Each criterion is based on visual assessment. However, it is not known what the inter-rater agreement of these criteria are. EEG is traditionally inspected in sensor space, i.e. in the recording channels. Advances in signal analysis made possible reconstructing the electric currents in the regions of the brain generating them, and displaying the signals in the source space, instead of the sensor space. The objectives of this study are: to determine the inter-rater agreement of the IFCN criteria by visual analysis in sensor space, to determine the combination of criteria with the best accuracy (sensitivity and specificity) and assess the accuracy of evaluating the discharges in source space. The raters will analyze EEG recordings from 100 patients, from two groups: consecutive patients with epilepsy and consecutive patients with non-epileptic paroxysmal episodes. EEG was recorded during long-term video-EEG monitoring. As reference standard, the investigators used the evaluation of the patients´ habitual clinical episode. The performance of the criteria in sensor-space and the analysis in source space will be compared with the unrestricted expert scorings.