Characteristics of Slow Waves on EEG Associated with Epileptic Spasms

Purpose: The high‐voltage slow waves (HVSs) on EEG associated with epileptic spasms were investigated to clarify their characteristics and their relation to the pathophysiology of spasms in West syndrome and related disorders. Methods: In 14 patients, digitally recorded EEG segments showing the ictal HVSs were extracted and their traces were overlaid by using an average reference. The ictal HVSs were also averaged to build maps for investigation of the pattern of potential distribution over the scalp. Results: In a total of 685 recorded spasms, 346 (50.5%) with minimal artifacts were selected to demonstrate that the ictal HVSs had a largely consistent waveform and distribution in each patient. The ictal HVSs were symmetrical in 10 patients and asymmetrical in the other four, and were relatively negative over the posterior region and positive over the frontal or temporal regions in 11 patients. Two symptomatic patients showed a marked deviation of the distribution of HVSs to the pathologically more involved hemisphere. An infant with Aicardi syndrome had two different types of spasms, each type showing a consistent pattern of HVSs with a lateralized distribution. Conclusions: The patterns of distribution of the ictal HVS may be related to the abnormal activation of the brain in the generation of spasms.