petit mal is a specific form of epilepsy, characterized by a transient, subtle impairment of consciousness, occurring mainly in children. By contrast with grand mal, it does not involve complete loss of consciousness, falling, and whole body convulsions. The condition is perhaps best epitomized by its alternative name, absence seizure. This denotes the period of some 3–30 seconds duration in which ongoing motor activities such as talking, eating, or walking cease and the sufferer stares ahead, seemingly unseeing, unhearing, and uncommunicative, and there may be automatism consisting of repeated but aimless movements; the eyelids may flicker at about three cycles per second. The actual level of awareness within episodes and between patients may differ, from one of total unresponsiveness to questions, to a limited ability to repeat number strings or names or a familiar recitation but no recollection of this at the end of the episode. In excess of thirty such ‘absences’ can occur in a day but may go unrecognized even by parents until such inattention becomes noticed at school.

A remarkable, in fact diagnostic, feature of petit mal is the generalized electrical seizure of the cerebral cortex that is detectable in the electroencephalogram (EEG) (or in its recent counterpart the electromagnetogram) recorded from electrodes on the overlying scalp. Unlike the normal, low amplitude rhythms of 20–50 microvolts, such as the alpha rhythm with a limited spatial distribution on the scalp, the electrical seizure is detected all over the scalp, is several fold greater in amplitude, and consists of bilaterally synchronous ‘spike and wave’ complexes repeating at about three times per second, with the spikes more prominent in the frontal regions. As well as accompanying an attack, brief episodes of such activity lasting 1–2 seconds can occur without overt behavioural signs, except brief hesitancies in counting that an investigator would seek to detect. The condition is of unknown cause and thus described as one form of idiopathic epilepsy; its onset is typically in childhood or early adolescence, the frequency of the episodes declining in adulthood, often to be replaced by more generalized convulsions.

Tom Sears

See also convulsions; epilepsy.