Absence seizure with generalized rhythmic delta activity.

In seven children, 5-11 years old, who presented with spells of staring or unresponsiveness, hyperventilation reproduced clinical spells that were accompanied on the EEG by generalized, rhythmic, delta activity. The discharges were usually of abrupt onset, extremely high amplitude, recurrent, and prolonged. One spontaneous staring spell, not provoked by hyperventilation, was also accompanied by generalized rhythmic delta activity. All patients had improvement or complete control of their spells and abolition of the EEG changes with ethosuximide or valproate. Delta activity during hyperventilation in children may not always be benign and may be associated with clinical absence seizures.