Abstracts

Rationale: EEG Source Imaging (ESI) of visually identified interictal spikes is useful to localize the epileptogenic zone (EZ). However, in all large cohort studies, the majority of patients had temporal lobe epilepsy. In this study we analyze the added value of automated spike detection followed by ESI to localize the EZ in patients with extra-temporal lobe epilepsy (ETLE). Methods: The long-term monitoring EEG of 19 ETLE patients recorded at the University Hospital of Geneva were analyzed using Epilog PreOp (Epilog NV, Gent, Belgium). The analysis consisted out of automated spike detection using the Persyst P13 software (Persyst Inc, California, US) followed by ESI using an advanced head model that contained 6 tissues. The detected spike clusters were visually scored to be genuine epileptic activity or of physiological nature by an expert electrophysiologist (VK) by looking at 10 individual events, the average waveform and the corresponding 2D topography at the peak. In the patients that had genuine spikes, the ESI localization of the peak of the spike cluster with most occurrences was compared with the surgery at lobar level. The sensitivity, specificity, positive predictive value, negative predictive value and odd’s ratio of the method to localize the EZ at lobar level were calculated. Results: In 4 of the 19 patients no genuine epileptic spikes were detected by the software. In the remaining 15 patients, the localization corresponded with the operated lobe in 6/8 patients that had Engel Class I outcome. In the poor outcome patients (Engel Class II, III and IV), the localization was discordant with the surgery in 6 of the 7 patients. This resulted in a sensitivity of 75%, specificity of 86%, PPV of 86%, NPV of 75% and an OR of 18. Conclusions: Automated spike detection and subsequent ESI showed lobar concordance in good outcome patients and not in bad outcome patients. This indicates that ESI of detected spikes can be used in the presurgical evaluation of ETLE patients. Nevertheless, the added value of ESI at sublobar level needs to be further investigated. Funding: This project received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 660230.