Association of fast ripples on intracranial EEG and outcomes after epilepsy surgery
Päivi Nevalainen, Nicolás von Ellenrieder, Petr Klimeš, François Dubeau, Birgit Frauscher, Jean Gotman
Abstract
<h3>Objective</h3> To examine whether fast ripples (FRs) are an accurate marker of the epileptogenic zone, we analyzed overnight stereo-EEG recordings from 43 patients and hypothesized that FR resection ratio, maximal FR rate, and FR distribution predict postsurgical seizure outcome. <h3>Methods</h3> We detected FRs automatically from an overnight recording edited for artifacts and visually from a 5-minute period of slow-wave sleep. We examined primarily the accuracy of removing ≥50% of total FR events or of channels with FRs to predict postsurgical seizure outcome (Engel class I = good, classes II–IV = poor) according to the whole-night and 5-minute analysis approaches. Secondarily, we examined the association of low overall FR rates or absence or incomplete resection of 1 dominant FR area with poor outcome. <h3>Results</h3> The accuracy of outcome prediction was highest (81%, 95% confidence interval [CI] 67%–92%) with the use of the FR event resection ratio and whole-night recording (vs 72%, 95% CI 56%–85%, for the visual 5-minute approach). Absence of channels with FR rates >6/min (<i>p</i> = 0.001) and absence or incomplete resection of 1 dominant FR area (<i>p</i> < 0.001) were associated with poor outcome. <h3>Conclusions</h3> FRs are accurate in predicting epilepsy surgery outcome at the individual level when overnight recordings are used. Absence of channels with high FR rates or absence of 1 dominant FR area is a poor prognostic factor that may reflect suboptimal spatial sampling of the epileptogenic zone or multifocality, rather than an inherently low sensitivity of FRs. <h3>Classification of evidence</h3> This study provides Class II evidence that FRs are accurate in predicting epilepsy surgery outcome.