This syndrome describes the triad of infantile spasms, psychomotor retardation, and hypsarhythmia on the EEG (Fig. 1,3A). The infantile spasms tend to occur infrequently during sleep (Kellaway et al., 1979; Gomez and Klass, 1983). Only 2-5% of the spasms occurred during sleep in the Kellaway series. The EEG abnormalities may be increased in NREM sleep and the hypsarhythmia pattern may become more apparent during sleep. Occasionally the hypsarhythmia pattern may be seen only during sleep (Jeavons and Bower, 1961). In some patients, bursts of spike and slow waves alternate with periods of generalized suppression of the EEG activity in a semiperiodic fashion, giving rise to a burst suppression-like pattern (Fig. 1.3B) (Passouant et al., 1975). During REM sleep, there is a marked attenuation or disappearance of the hypsarhythmia pattern (Jeavons and Bower, 1961).
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