Absence seizures in children: clinical and electroencephalographic features.

The clinical and electroencephalographic (EEG) features of absence seizures in children were evaluated using EEG frequency modulation radiotelemetry and videotape monitoring. The only seizures evaluated were those with a spike-and-wave or multiple spike-and-wave duration lasting at least 3 seconds. A total of 926 absence seizures (426 typical, 500 atypical) were reviewed in 54 patients. Abnormal interictal EEGs, multiple seizure types, mental retardation, or developmental delay were more likely in patients with atypical absence seizures than in patients with typical absence seizures. Both types of absence seizures usually had a clear onset and cessation. Atypical absence seizures lasted significantly longer than did typical absence seizures. Automatisms occurred more frequently in typical absence seizures than in atypical ones, while decreases in postural tone or tonic activity occurred more frequently in atypical absence seizures. Receptive and expressive speech were retained in some patients during both types of seizures. This study demonstrates that typical and atypical absence seizures are not discrete entities but rather form a continuum. No single clinical feature can adequately distinguish the two seizure types.