They are usually spontaneous, but can be triggered by photic, pattern, video games stimuli, and mental or emotional factors. Typical absences are easily precipitated by hyperventilation in about 90% of untreated patients. The intradischarge frequency may be constant or may vary (2.5 to 5Hz). The ictal EEG discharge may be consistently brief (2 to 5 seconds) or long (15 to 30 seconds), continuous or fragmented, with single or multiple spikes associated with the slow wave. Clonic, tonic and atonic components alone or in combination are motor symptoms myoclonia, mainly of facial muscles, is the most common. This is often associated with motor manifestations, automatisms and autonomic disturbances. Impairment of consciousness may be severe, moderate, mild or inconspicuous. Their clinical and EEG manifestations are syndrome-related. They differ fundamentally from other seizures and are pharmacologically unique. They have 2 essential components: clinically, the impairment of consciousness (absence) and, generalised 3 to 4Hz spike/polyspike and slow wave discharges on electroencephalogram (EEG). Typical absences are brief (seconds) generalised seizures of sudden onset and termination.
