Abstracts

Rationale: Although focal lesions can generate epileptic spasms in humans and in animal models, the classical ictal EEG correlate in epileptic spasms is electrodecremental response, which usually has generalized appearance. High frequency ictal activity with frequencies of 40 Hz or greater is considered important in the generation of seizures. Here we hypothesized that localized higher frequency activity may be recruited to drive epileptic spasms.Methods: A total of 1033 spasms from 34 patients with West syndrome of various etiologies were analyzed in video-EEG using time-frequency analysis. Spatial and temporal characteristics of ictal gamma activity (40 - 90 Hz) on scalp EEG were investigated in relation to visual symmetry of spasms, objective EMG (electromyography) analysis, and etiology of WS.Results: During spasms, there was a channel-specific ictal augmentation of gamma activity at 40 - 90 Hz (mean onset frequency 68.1 Hz) around the centroparietal channels (C3-P3 and C4-P4) prior to ictal motor manifestations regardless of the underlying etiology. The mean maximal augmentation of gamma activity at these centroparietal channels was more prominent compared to that of the beta activity (known etiology: 412% vs 223% [p=0.002], unknown etiology: 518% vs 237% [P < 0.001]). The ictal gamma activity occurred on average 260 ms prior to the EMG onset [95% CI: 330 - 190 ms]. This ictal gamma activity was closely related to semiology; unilaterally enhanced gamma activity in the centroparietal channels correlates with visually asymmetric semiology, and this correlation was not observed in ictal beta activity. Unilaterally enhanced ictal gamma activity is consistent with presence of known/localized pathology. The maximal augmentation of ictal gamma activity at the centroparietal channels decreased with age, while ictal beta activity (15 - 30 Hz) did not show such correlation with age.Conclusions: Focal ictal gamma activity in the centroparietal channels seems to drive the motor manifestations in epileptic spasms in WS. Epileptic spasms may be a seizure with a focal onset near the centroparietal channels regardless of the underlying etiology. Ictal gamma activity may potentially be used as age-specific biomarker to identify seizure onset of epileptic spasms in selected cases.