Behavioral and EEG asymmetry and asynchrony of 8,680 infantile spasms were analysed in a review of 75 consecutive video-EEG recordings performed at UCLA Medical Center, Los Angeles from 1982 to 1992. Asymmetry occurred in 25% and asynchrony in 7% of recorded spasms. The seizure EEG discharge was usually contralateral to the clinically involved side. In 12 of 60 patients (20%), more than 50% of recorded spasms were asymmetric or asynchronous. This group of patients showed the most frequent structural and functional brain abnormalities involving the contralateral central region detected by EEG, MRI, PET, and neurological examination. Partial seizures with lateralized motor behavior occurred in 50% of this group compared to only 9% of patients showing asymmetry-asynchrony in less than one third of spasms. Partial seizures were associated with clusters of infantile spasms in 35% of the children in the study. 
COMMENT. The authors suggest that this combination of asymmetric and/or asynchronous infantile spasms, partial motor seizures involving the same side of the body, and contralateral central region pathology may represent a previously undescribed and unique subset of symptomatic age-specific localization-related infantile epilepsy. The findings support the hypothesis that infantile spasms are generated by the cerebral cortex and the primary sensorimotor cortex is involved in asymmetric and asynchronous spasms.