Reappraisal of interictal electroencephalograms in infantile spasms

To delineate interictal electroencephalographic (EEG) features before treatment of patients with clinically defined infantile spasms, EEGs of 82 infants having tonic spasms in clusters were analyzed by type of paroxysmal abnormalities, continuity, interhemispheric synchrony, topography, and wave component of hypsarrhythmia during wakefulness and sleep. Hypsarrhythmia occurred less frequently in wakefulness than in non-rapid eye movement (NREM) sleep at any age, least frequently in wakefulness after 1 year of age, and disappeared in rapid eye movement (REM) sleep at any age. The continuity of hypsarrhythmia changed with states, but did not change with age, and was greatest in wakefulness and stage 1 and decreased in stage 2-3. Interhemispheric synchrony increased with increasing age but decreased with advancing sleep stage. The term modified hypsarrhythmia should be discarded, and unusual features, if present, should be specified.