Ictal electroencephalographic activity in West syndrome

Abstract

Epileptic spasm in West syndrome (WS) have unique clinical and EEG pattern. Usually ictal EEG shows high voltage slow wave during epileptic spasms or superimposed spindle-like fast activity of medium amplitude and a decremental activity. The spindle-like activity occurred either isolated, generally at the beginning or the end of a cluster or immediately before the slow wave. The decremental activity, correspond to a post ictal pattern following the slow waves. We selected EEGs od 25 infants having WS, followed for at least 10 years. Symmetric spasms were present in cryptogenic and symptomatic patients. Asymmetric spasms, and/or focal signs during spasms, strongly indicated existence of a cerebral lesion. In both etiological groups, the characteristic ictal EEG pattern of the spasms consisted of a positive-vertex slow wave. Fast activity (spindle-like), and decremental activity were also present. The consistent lateralization of the ictal EEG events correlated with EEG beta-activity. We considered it as indicating local cortical dysfunction in infants who fail to respond to early treatment and often progress toward severe epilepsy. Although independent from the etiology of the spasms, persisting hypsarrhythmia during a cluster of spasms appeared as an EEG pattern that correlated with a favorable outcome.