Extreme somatosensory evoked potential (ESEP): an EEG sign forecasting the possible occurrence of seizures in children.
In a population of 15,000 children it was found that tactile stimulation, mainly tapping on the soles or heels of the feet, could elicit high-voltage evoked potentials in the EEGs of 1% of them. A longitudinal study of 16 of these patients showed a stereotyped electroclinical evolution. At first, only extreme somatosensory evoked potential (ESEPs) were observed in nonepileptic children with normal EEG records (first period). Then, after a variable delay, spontaneous EEG abnormalities appeared, first only during sleep, and then also during wakefulness, usually as spikes involving the same parietal and midline regions where the ESEPs were evident (second and third periods). Seizures then began (fourth period) within 5 months to 2 years after the appearance of the interictal focal abnormalities. Such seizures were rare, but in some cases they were grouped in bouts that amounted to status epilepticus. The seizures were usually of the partial motor type, with adversion of the head, but infrequently they assumed the tonic-clonic type; they occurred mainly during the daytime. The fits were short-lived, however, and after a year had mostly disappeared, while the ESEPs and spontaneous interictal focal abnormalities sometime persisted for several year before disappearing, too. The subjects were otherwise neurologically and psychologically normal throughout the observation and follow-up period.