Absence seizures (also called petit mal seizures) are lapses of awareness, sometimes with staring, that begin and end abruptly, lasting only a few seconds. There is no warning and no after-effect. More common in children than in adults, absence seizures are frequently so brief that they escape detection, even if the child is experiencing 50 to 100 attacks daily. They may occur for several months before a child is sent for a medical evaluation.
More common in children than in adults, absence seizures almost always start between ages 4 and 12 years, and rarely do they begin after age 20. Absence seizures are characterized by a brief impairment of consciousness, which usually lasts no more than a few seconds. The child, whether sitting or standing, simply stares vacantly; neither speaking nor apparently hearing what is said. Then, as abruptly as it began, the impairment lifts and the child continues with his or her previous activity. However, a brief segment of unawareness has been imposed in the stream of activity or thought. Automatisms may occur in prolonged absence seizures. Absence seizures are frequently so brief that they escape detection, even if the child is experiencing 50 to 100 attacks daily. They may occur for several months or even years before a child is sent for a medical evaluation.
Some absence seizures are accompanied by brief myoclonic jerking of the eyelids or facial muscles, or by variable loss of muscle tone. More prolonged attacks may be accompanied by automatisms, which may lead them to be confused with complex partial seizures. However, complex partial seizures last longer, may be preceded by an aura, and are usually marked by some type of confusion following the seizure.
Absence seizures may occur only occasionally or more than 100 times a day. Most children with typical absence seizures are otherwise normal. Although manifestations of their seizures are usually subtle, these children need prompt and effective treatment because absence seizures can interfere with learning. About half the children also have infrequent generalized tonic-clonic seizures. The electroencephalographic (EEG) pattern of diffuse spike-wave is closely correlated with absence seizures.
Absence seizures are often confused with complex partial seizures. This is an unfortunate mistake because the drugs that prevent absence seizures have little or no effect on complex partial seizures. Conversely, the most effective drugs for complex partial seizures are either ineffective against or increase the frequency of absence seizures.
Although absence and complex partial seizures can be confused, they have distinct differences. First, absence seizures are never preceded by an aura. Second, absence seizures are of briefer duration – seconds rather than minutes. Third, absence seizures begin frequently and end abruptly. Finally, the absence attack is always associated with the strikingly typical EEG abnormality of spike and slow wave discharges, usually at a frequency of 3Hz. These discharges can occur interictally and ictally and are often provoked by hyperventilation.