Interictal high frequency oscillations (HFOs) in patients with focal epilepsy and normal MRI

ObjectiveWe aim to analysis the relationship between HFOs-generating regions and the seizure onset zone (SOZ) in epileptic patients without a visible lesion on MRI.MethodsIntracerebral EEGs were recorded in 17 patients with intractable focal seizures and normal MRIs. The rates of interictal HFOs and spikes inside and outside the SOZ were analyzed as well as the specificity, sensitivity and accuracy of HFOs and spikes to determine the SOZ.ResultsThe mean rate of spikes, ripples and fast ripples (FR) was higher in the SOZ than in the non-SOZ channels. In regard to the identification of the SOZ the sensitivity was 91% for spikes, 91% for ripples and 66% for FR, the specificity was 30% for spikes, 42% for ripples and 80% for FR, and the accuracy was 44% for spikes, 54% for ripples and 76% for FR.ConclusionsThe rates of spikes and HFOs were higher inside than outside the SOZ. However, HFOs are also more specific and accurate than spikes to delineate the SOZ.SignificanceAnalysis of interictal HFOs during 5–10 min of sleep recording is a good tool to localize the SOZ in patients with epilepsy and normal MRI, and could potentially reduce the duration of chronic intracerebral EEG recordings.

► We demonstrated, for the first time, that interictal high frequency oscillations (HFOs) can be used to localize the seizure onset zone (SOZ) in a group of patients with epilepsy and normal MRI. ► Fast ripples and ripples are more specific and accurate than spike to delineate the SOZ in patients with epilepsy and normal MRI. ► In non-lesional epileptic patients with more than one SOZ there were no significant differences between the leading and the secondary SOZ regarding the rates of HFOs.