Simultaneous recording of absence seizures with video tape and electroencephalography. A study of 374 seizures in 48 patients.

Forty-eight patients, 4 to 24 years of age, with recurring absence seizures were studied prospectively for twenty-seven months. Each patient and his EEG were recorded simultaneously by a multicamera videotape technique and each recording was repeatedly viewed and described in writing by two observers who subsequently resolved any differences by joint viewing. From the 48 patients, 374 clinical absence seizures were recorded and classified according to the International Classification of Epileptic Seizures. Automatisms accompanied at least one attack in 88 per cent of the patients. Mild clonic components occurred in 71 per cent, and decreased postural tone in 41 per cent. Only one patient experienced an attack comprising only "blank staring" accompanied by unawareness and amnesia, but 40 per cent of patients exhibited this type of attack in addition to more complex absence attacks. Seizures of ten seconds or less in duration occurred among 85 per cent of patients. Each of the 374 seizures were readily classified according to the International Classification, but simple absence constituted only 9-4 per cent of the seizures. The others most often contained, in order of prevalence, either automatisms, mild clonic components, or decreased postural tone, or a combination of two or more of these features. The relationship between increased duration of the seizures and the occurrence of automatisms was significant. The findings are discussed in relation to differential diagnosis and mechanisms of automatisms. Absence seizures differ from complex partial (temporal lobe, psychomotor) seizures because an aura does not precede the abruptly beginning absence attack, the seizure usually lasts less than ten seconds, and mental clarity returns instantly at the end of the seizure.