Abstracts

RATIONALE: What is the current contribution of scalp EEG in presurgical evaluation? METHODS: Retrospective analysis of scalp and intracranial EEG findings and rates of utilization in consecutive patients evaluated for epilepsy surgery at one center. RESULTS: Over an 18 year period from 1982, the rate of intracranial EEG utilzation declined from a high of 60% between 1986 and 1990, to 29% between 1995 and 1999. In 3 years between 1994 and 1996, 278 patients underwent prolonged video-EEG monitoring and 160 had confirmed epilepsy. In the same time period, 55 received epilepsy surgery. Of the latest 90 patients who received focal resections, scalp EEG recorded localized slowing in 56 (62%) with 42 (47%) localizable to one lobe. Epileptiform discharges were seen in 82 (91%) with 64 (71%) localizable to one lobe. Unilateral (99% predominant) temporal slowing (in 40) or spikes (in 58) always agreed with the side of eventual temporal resection. Bitemporal spikes were found in 8. Spikes were mislocalizing or misleading in 3. Scalp ictal patterns were recorded in 89 patients, 62 (69%) localized to one lobe, 12 (13%) lateralized to one hemisphere, 4 (4%) bifocal or multifocal, and nonlocalized in 11 (12%). There was no instance where a localized or lateralized ictal onset pattern pointed to the wrong side. CONCLUSIONS: Scalp EEG interictal and ictal monitoring remain indispensable in presurgical evaluation. It helps separate surgical candidates from those with other forms of epilepsy or nonepileptic conditions. Localizing or lateralizing EEG information is found in almost 80%. When used in conjunction with modern imaging techniques, many patients can be selected for surgery noninvasively.