Interictal, unifocal spikes in refractory extratemporal epilepsy predict ictal origin and postsurgical outcome

Objectives: To evaluate the significance of exclusively unifocal, unilatera l, interictal epileptiform patterns on scalp electroencephalography (EEG) i n surgical candidates with medically intractable extratemporal epilepsy. Methods: We reviewed 126 patients with refractory extratemporal partial sei zures who underwent epilepsy surgery at our center. All were followed for a t least 2 years after resections. Surgery was based on ictal EEG recordings . We examined ictal onsets and surgical outcome in subjects whose preoperat ive, interictal scalp EEGs during long-term monitoring (LTM) demonstrated o nly unilateral, well-defined focal discharges, and outcome in patients whos e interictal EEGs during LTM showed bilateral, non localized, or multifocal epileptiform patterns. Results: We found that 26 subjects exhibited only unilateral, unifocal, int erictal epileptiform patterns. In all 26 cases (100%) clinical seizures aro se from the regions expected by the interictal findings (P < 0.0001, Sign t est). At last follow-up 77% (20/26) of these patients were seizure-free, wh ile 23% (6/26) had >75% reduction in seizures. This compares to the remaini ng patients, of whom 34% (34/100) were seizure-free, 42% (41/100) had >75% reduction in seizures, and 25% (25/100) had <75% reduction in seizures (P = 0.0001, Fisher's Exact test). Conclusions: Strictly unifocal, interictal epileptiform patterns on scalp E EG, though seen in a minority of subjects, may be an important. independent factor in evaluating subjects with intractable extratemporal, localization -related epilepsy for surgical therapy. This finding is highly predictive o f both ictal onsets and successful postsurgical outcome. (C) 2000 Elsevier Science ireland Ltd. All rights reserved.