Fast oscillation dynamics during hypsarrhythmia as a localization biomarker.

Hypsarrhythmia in West syndrome, although hard to define, is characterized by chaotic and disorganized electrical activity of the brain and is often regarded as a generalized EEG pattern without any localization value. Using event-related spectral perturbation (ERSP), we tried to determine the brain dynamics during hypsarrhythmia. Routine 1-h scalp EEGs were retrieved from 31 patients with infantile spasms and 20 age-matched controls. Using the EEGLAB toolbox of MATLAB 2015b, the ERSPs of fast oscillations (FOs; 20-100 Hz) of selected channels were analyzed and compared among groups according to their MRI lesions. FO-ERSP cutoff values for predicting the pathologic foci were estimated. The mean FO-ERSPs across all analyzed electrodes of patients with spasms were significantly higher than those of controls. When the patients were categorized into nonlesional, focal/multifocal, or diffuse lesional groups, the FO-ERSP of patients in the focal/multifocal lesional group was significantly lower than that of those in the nonfocal or diffuse lesional groups. In the focal/multifocal lesional group, seven patients (7/9, 77.8%) showed that the locations of channels with high FO-ERSPs were matched to the pathologic MRI lesions. Thus, the localization of high FO-ERSPs is closely associated with the location of pathologic brain lesions. Further research is required to prove the value of the FO-ERSP as an important quantitative localizing biomarker of West syndrome. NEW & NOTEWORTHY The locations of high fast oscillation-event-related spectral perturbations (FO-ERSPs) are closely associated with brain pathologic lesions, and high FO-ERSPs can be used as a localization biomarker of pathologic brain lesions in patients with hypsarrhythmia. With further validation, FO-ERSP might be useful as a biomarker for the localization of hidden pathologies in conditions with generalized epileptiform activities such as West syndrome.