Early electroclinical manifestations and treatment responses were evaluated by video-EEG in 44 infants with infantile spasms. Mean ages at onset and at first video-EEG were 5.3 and 5.9 months, respectively. Etiology was cryptogenic in 13 and symptomatic in 31 infants. Vigabatrin was the initial treatment in 36, and all infants were followed until 12 months of age. On the first video-EEG before treatment, 27 infants showed hypsarrhythmia, and 17 had multifocal spikes with normal EEG background. A 4-hour recording including waking, sleep, and awakening was usually sufficient to detect spasms. Subtle, asymmetric or asynchronous spasms, and asymmetric ictal or interictal EEG abnormalities were associated with symptomatic etiology and poor cognitive and seizure outcome. Treatment modifies both spasms and EEG; spasms may become subtle and only discernible on EEG, and hypsarrhythmia may be replaced by multifocal spikes. Hypasarrhythmia rarely persists following vigabatrin treatment. Complete eradication of spasms, including subtle variants, is essential for a favorable cognitive outcome. 
COMMENT. Video-EEG may be essential for the initial diagnosis of infantile spasms, especially in infants with symptomatic etiology and subtle spasms. It is also necessary in assessing response to treatment and the exclusion of persisting subtle spasms not clinically evident.