Interictal High Frequency Oscillations Indicate Seizure Onset Areas In Focal Epilepsy Patients

Epilepsy is a common, chronic neurological condition and data suggested that30-40%patients were medically refractory epilepsy. Patients with intractable partialepileptic seizures can be treated with surgery and delineate the epileptogenic zone (EZ)is important for obtaining a good outcome. Now, there is not a reliable indicator for EZ,such as irritative zone, seizure onset zone (SOZ), symptomatogenic zone, functionaldeficit zone or structural epileptogenic lesion. High frequency oscillations (HFOs) werea major discovery in epilepsy research and were found in rodents as well as in humanswith hippocampal sclerosis. We proposed the following hypothesis that the localizationof interictal HFOs during intracranial EEG recording in neocortical epilepsy was anindicator to the EZ also.In this study, patients with invasive EEG recording were included. The follow-upof post-operation was at least2years and outcome was Engle â… or â…¡. IntracranialEEGs were recording using the g.tec monitoring system sample at2400Hz. Weobtained at least1night good data and analyzed10minutes samples during slow-wavesleep. Spikes and HFOs were visually marked and SOZ was defined by anotherelectroencephalographer. We analyzed the difference of the rates of spikes and HFOsand the number of channels with spikes and HFOs inside SOZ and outside SOZ. Also,we wanted to know the sensitivity, specificity and accuracy of spikes, ripples and fastripples to localize the SOZ. We found the mean rate of interictal spikes and HFOs werehigher in the SOZ than in the non-SOZ. The proportion of channels showing spikes,ripples and fast ripples was higher inside than outside SOZ. To indicate the SOZ, thesensitivity was83.8%for spikes,78.8%for ripples and52.5%for fast ripples. Thespecificity was50.9%for spikes,65.7%for ripples and87.0%for fast ripples, theaccuracy was56.0%for spikes,67.7%for ripples and81.8%for fast ripples.HFOs can be detected in neocortical epilepsy and mesial temporal lobe epilepsyusing macroelectrodes. HFOs were recording simultaneously more than3contacts, thissuggested that HFOs may result from a large neuronal synchrony scale. HFOs weremore specific and accurate than spikes for the SOZ, so HFOs related cortex should beresected during the surgery. Analysis of interictal HFOs was good to localize the SOZ in epilepsy patients, and may reduce the duration of chronic intracranial EEG recordingsand lower the probability of intracranial infection.