Lateralizing Seizure Onset Zone Through Interictal Sleep Scalp EEG High-Frequency Oscillations

Epilepsy, a neurological disorder impacting an estimated 50 million people globally, sees about 30% of patients developing drug-resistant epilepsy (DRE). For these patients, surgery emerges as a more promising option for achieving seizure freedom. The precise delineation of the Epileptogenic Zone (EZ) is crucial for considering a patient as a surgical candidate, with the Seizure Onset Zone (SOZ) considered the most reliable estimate of the EZ. In this retrospective study, we analysed interictal sleep electroencephalography (EEG) data from 5 patients to evaluate the rate of High-Frequency Oscillations (HFOs) in the 80-250 Hz range. Our objective was to explore whether regions exhibiting a higher incidence of HFO rates correlated with those diagnosed as the SOZ based on patient reports. Additionally, we computed the asymmetry index to examine whether the heightened HFO rate lateralizes to the hemisphere where the seizure occurs. Our results revealed a precise correlation between elevated HFO rates in a region and the specified SOZ as per the report in 4 out of 5 patients. Furthermore, the asymmetry index consistently lateralized to the same hemisphere causing seizure as specified in the report a cross all 5 patients. This implies that the analysis of HFOs can provide valuable assistance to clinicians in accurately identifying the hemisphere responsible for seizures.