Scalp EEG Ictal gamma and beta activity during infantile spasms: Evidence of focality

Abstract

Objective We investigated temporal and spatial characteristics of ictal gamma and beta activity on scalp EEG during spasms in patients with West syndrome (WS) to evaluate potential focal cortical onset. Methods A total of 1033 spasms from 34 patients with WS of various etiologies were analyzed in video-EEG using time-frequency analysis. Ictal gamma (35–90 Hz) and beta (15–30 Hz) activities were correlated with visual symmetry of spasms, objective EMG (electromyography) analysis, and etiology of WS. Results Prior to the ictal motor manifestation, focal ictal gamma activity emerged from one hemisphere (71%, 24/34) or from midline (26%, 9/34), and was rarely simultaneously bilateral (3%, 1/34). Focal ictal beta activity emerged from either one hemisphere (68%, 23/34) or from midline (32%, 11/34). Onsets of focal ictal gamma and beta activity were most commonly observed around the parietal areas. Focal ictal gamma activity propagated faster than ictal beta activity to adjacent electrodes (median: 65 vs. 170 ms, p<0.01), and to contralateral hemisphere (median: 100 vs. 170 ms, p=0.01). Asymmetric peak amplitude of ictal gamma activity in the centroparietal areas (C3-P3 vs. C4-P4) correlated with asymmetric semiology. On the other hand, the majority of visually symmetric spasms showed asymmetry in peak amplitude and interhemispheric onset latency difference in both ictal gamma and beta activity. Significance Spasms may be a seizure with focal electrographic onset regardless of visual symmetry. Asymmetric involvement of ictal gamma activity to the centroparietal areas may determine the motor manifestations in WS. Scalp EEG ictal gamma and beta activity may be useful to demonstrate localized seizure onset in infants with WS.

Increased electroencephalography connectivity precedes epileptic spasm onset in infants with tuberous sclerosis complex

“…[17][18][19][20] However, it is also possible that ES have a focal onset with rapid spread throughout the brain. 21 One study showed that infants with West syndrome and hypsarrhythmia had increased long-range EEG coherence in multiple frequency bands in sleep after onset of ES. 22 Another study showed that infants after ES onset had decreased longrange temporal correlation in the beta band of awake EEG.…”

Interrater reliability in visual identification of interictal high‐frequency oscillations on electrocorticography and scalp EEG

“…[4][5][6][7] In contrast to ECoG, the identification of HFOs with noninvasive scalp electroencephalography (EEG) has proven more challenging. Although several studies have linked beta, gamma, and ripple activity to hypsarrhythmia 8 and epileptic spasms 9,10 in West syndrome, and to the seizure-onset zones in focal epilepsy, 11 it is only recently that fast ripples (FRs) have been identified with the use of subdermal scalp electrodes in adults with epilepsy, 12 and with the use of standard scalp electrodes in children with epilepsy. 13 Nevertheless, it has not yet been established that the visual identification and quantification of scalp HFOs is reliable.…”

Scalp EEG interictal high frequency oscillations as an objective EEG biomarker of infantile spasms

“…Although prior studies have reported the presence of scalp EEG gamma band (30-80 Hz) and ripple band (80-250 Hz) activity in infantile spasms (Kobayashi et al, 2004;Kobayashi et al, 2015;Nariai et al, 2017), this is the first study to report that a fast ripple band (250-500 Hz) is seen on scalp EEG in children with infantile spasms. Recently our group reported for the first time that scalp EEG fast ripples could be seen in children with drug-resistant epilepsy with tuberous sclerosis complex (TSC) .…”

“…. The values range from -1 (values on the left hemisphere being disproportionally large) to +1 (values on the right hemisphere being disproportionally large) (Nariai et al, 2017). We compared the absolute asymmetric indices (abs AI) of HFOs (80-500 Hz) rate, MI of HFOs (80-500 Hz) & SWA (3-4 Hz and 0.5-1 Hz) between subjects with and without focal lesion on MRI.…”

“…Recent studies have shown EEG fast activities can be recorded non-invasively from the scalp recordings (Andrade-Valenca et al, 2011;Bernardo et al, 2018;Kobayashi et al, 2004;Kobayashi et al, 2015;Kramer et al, 2019;Nariai et al, 2017;Nariai et al, 2018;Pizzo et al, 2016;Wu et al, 2008). Scalp EEG HFOs have the potential to localize seizure onset zones (Andrade-Valenca et al, 2011;Bernardo et al, 2018;Nariai et al, 2017;Tamilia et al, 2020), and to monitor disease activity in epileptic spasms (Kobayashi et al, 2015), Rolandic epilepsy (Kobayashi et al, 2011;van Klink et al, 2016), and epileptic encephalopathy with continuous spike-and-wave during sleep (CSWS) (Cao et al, 2019;Kobayashi et al, 2010). Additionally, HFOs coupled with slow-wave activity strongly localize to epileptic brain regions in children with infantile spasms and other types of focal epilepsy in invasive monitoring (Iimura et al, 2018;Motoi et al, 2018;Nonoda et al, 2016;Song et al, 2017;Weiss et al, 2016) and may reflect disease activity in scalp EEG in epileptic spasms (Bernardo et al, 2020.…”