Phase Lag Analyses on Ictal Scalp Electroencephalography May Predict Outcomes of Corpus Callosotomy for Epileptic Spasms

Abstract

Objective: We aimed to clarify the patterns of ictal power and phase lag among bilateral hemispheres on scalp electroencephalography (EEG) recorded pre-operatively during epileptic spasms (ESs) and the correlation with the outcomes following corpus callosotomy.Methods: We enrolled 17 patients who underwent corpus callosotomy for ESs before 20 years of age. After corpus callosotomy, seven patients did not experience further ESs (favorable outcome group), and the remaining 10 patients had ongoing ESs (unfavorable outcome group). We used pre-operative scalp EEG data from monopolar montages using the average reference. The relative power spectrum (PS), ictal power laterality (IPL) among the hemispheres, and phase lag, calculated by the cross-power spectrum (CPS) among symmetrical electrodes (i.e., F3 and F4), were analyzed in the EEG data of ESs from 143 pre-operative scalp video-EEG records. Analyses were conducted separately in each frequency band from the delta, theta, alpha, beta, and gamma range. We compared the means of those data in each patient between favorable and unfavorable outcome groups.Results: Among all frequency bands, no significant differences were seen in the individual mean relative PSs in the favorable and unfavorable outcome group. Although the mean IPLs in each patient tended to be high in the unfavorable outcome group, no significant differences were found. The mean CPSs in the delta, theta, and gamma frequency bands were significantly higher in the unfavorable than in the favorable outcome group. Using the Youden index, the optimal cutoff points of those mean CPS values for unfavorable outcomes were 64.00 in the delta band (sensitivity: 100%, specificity: 80%), 74.20 in the theta band (100, 80%), and 82.05 in the gamma band (100, 80%). Subanalyses indicated that those CPS differences originated from pairs of symmetrical electrodes in the bilateral frontal and temporal areas.Significance: Ictal power and laterality of the ictal power in each frequency band were not associated with the outcomes of CC; however, the phase lags seen in the delta, theta, and gamma frequency bands were larger in the unfavorable than in the favorable outcome group. The phase lags may predict outcomes of CC for ESs on pre-surgical scalp-ictal EEGs.

Corpus Callosotomy for Controlling Epileptic Spasms: A Proposal for Surgical Selection

“…Of these, three patients achieved seizure freedom with CC only, and two achieved seizure freedom through additional treatments [9]. In the patients with partial response in those previous studies, CC achieved reduction of seizure frequency and/or changed the ES into smaller ones, like head nodding or resolving drop attacks, unilaterally focal onset ES, or bilaterally independent focal onset-ES [3,4,6,[8][9][10][11][12]61,71]. Large data of long-term outcomes of CC for ES is unavailable.…”

“…In these cases, ictal EEG is visually bilateral and synchronous on slow waves [10]. Computed frequency analyses of presurgical scalp EEG recordings have shown small phase lags of ictal slow and beta waves among the bilateral hemispheres and less power and connectivity on interictal records [8,11]. caused predominantly by unilateral cortices and tend to show a uniformly lateralized seizure type.…”

“…The analysis for spatial concordance between fast and slow EEG activity indicated subcortical contribution in the emergence of ES [ 53 ]. Interhemispheric modulation and recruitment of epileptic excitations via the corpus callosum are necessary for the emergence of at least some part of the ES [ 10 , 11 , 12 ]. The etiology is multiple and diverse and has been classified as structural, genetic, infectious, metabolic, immunological, or involving unknown conditions [ 54 ].…”

“…Some studies have not provided particular details concerning the efficacy of CC procedures to treat ES or West syndrome, but have reported whole outcomes including patients with other types of seizures, Lennox-like syndrome, or Lennox-Gastaut syndrome [ 64 , 65 , 66 , 67 , 68 , 69 ]. However, in other recent studies, the outcomes of CC to treat ES, which mostly involved patients with West syndrome, have been presented using detailed patient data [ 3 , 4 , 6 , 8 , 9 , 10 , 11 , 70 ]. Because of these studies, CC use has been adapted to not only involve treatment for drop attacks (tonic seizures, atonic seizures) and atypical absence and tonic–clonic seizures, but also for patients with ES, and for older patients with Lennox-Gasutaut syndrome and Lennox-like syndrome, as well as infants with West syndrome, regardless of the presence of the sudden falling-down manifestation.…”

“…Since then, CC has been applied for the treatment of drop attacks, which were classified into generalized tonic or atonic seizures in the latest classification of seizure types in 2017 by the International League Against Epilepsy (ILAE). However, CC has also been adopted for the treatment of epileptic spasms (ES), as reported by Pinard in 1993 [ 2 ], and reports concerning CC for the treatment of patients with ES has increased since 2010 [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ].…”