Spectral properties of EEG fast activity ictal discharges associated with infantile spasms

Objective: The aim of this study was to evaluate the characteristics of the ictal EEG event accompanying infantile spasms. Methods: Quantitative analysis was used, based on the application of a biva riate autoregressive (AR) parametric model; autospectra, coherence, phase f unctions and inter-hemispheric time differences were estimated on homologou s EEG channels in 18 infants presenting with either cryptogenic or symptoma tic West syndrome. Results: The AR analysis of the 500 ms EEG epochs preceding spasm onset rev ealed the presence of a short discharge of fast activity restricted to a na rrow frequency band in 13 of the 18 cases included in the study. The fast d ischarge peaked at 17.5 +/- 2.1 Hz, with rather low inter-hemispheric coher ence values (0.52 +/- 0.17) and asymmetric amplitude on homologous EEG deri vations. It persisted briefly after spasm onset, reaching a higher coherenc e value (0.71 +/- 0.16). The inter-hemispheric time difference, estimated i n those cases with the coherence values significantly different from zero, ranged from 9.1 to 14.3 ms (11.4 +/- 1.9) in the epoch preceding spasm onse t. Conclusion: The data obtained from the analysis of the ictal EEG events, co mpared with clinical and interictal EEG features, indicate that an asymmetr ic EEG pattern (mainly consisting of a rhythmic burst of fast activity) con sistently preceded both symmetric and asymmetric spasms, thus suggesting a localized cortical origin of the ictal discharge giving rise to the spasms. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.