Interictal ripples nested in epileptiform discharge help to identify the epileptogenic zone in neocortical epilepsy

Objective: This study aimed to identify the subtype of interictal ripples that help delineate the epileptogenic zone in neocortical epilepsy.

Methods: Totally 25 patients with focal neocortical epilepsy who had invasive electroencephalography (EEG) evaluation and subsequent surgery were included. They were followed up for at least 2years. Interictal ripples (80-250Hz) and fast ripples (250-500Hz) during slow-wave sleep were identified. Neocortical ripples were defined as type I ripples when they were superimposed on epileptiform discharges, and as type II ripples when they occurred independently. Resection ratio was calculated to present the extent to which the cortical area showing an interictal event or the seizure onset zone (SOZ) was completely removed.

Results: Fast ripples and types I and II ripples were found in 8, 19, and 21 patients, respectively. Only the higher resection ratio of interictal fast or type I ripples was correlated to the Engel 1a surgical outcome.

Conclusions: Type I ripples could assist in localizing the epileptogenic zone in neocortical epilepsy.

Significance: Type I and fast ripples both may be pathological high-frequency oscillations.