UNILATERAL FOCAL PREPONDERANCE OF INTERICTAL EPILEPTIFORM DISCHARGES AS A PREDICTOR OF SEIZURE ORIGIN

Objective: To test the hypothesis that seizure origin may be predicted from scalp-recorded electroencephalographic interictal epileptiform p atterns that occur exclusively or preponderantly over a single focal r egion. Patients and Methods: Fifty-nine of 98 patients (greater than o r equal to 16 years old) with intractable epilepsy who underwent sphen oidal/scalp electroencephalographic video monitoring were identified a s having interictal epileptiform discharges preponderantly (greater th an or equal to 75% of all discharges) or exclusively over a single uni lateral region (basal-temporal, midposterior temporal, frontopolar, su perior frontal, central). Ictal recordings in 48 patients could be int erpreted as demonstrating focal origins, and the ictal findings were c ompared with the interictal findings. Eleven patients had uninterpreta ble ictal recordings or no seizures during monitoring and were not fur ther considered. Results: All seizures arose from the expected region in 39 of the 48 patients (Fisher's exact test, P<.001). Interictal dis charges occurred exclusively over a single region in 23 of the 48 pati ents, and all seizures arose from the expected region in 22 of the 23 patients (P<.001). Seventeen patients among this group of 23 had exclu sively unilateral basal-temporal discharges, and all seizures arose fr om the expected side, with the exception of one seizure that arose fro m the opposite side in one patient, with her other seizure arising fro m the expected side (P<.001). All seizures arose from the expected reg ion in three patients who exhibited all interictal discharges arising from a single superior frontal region, in two patients with discharges only over a single midposterior temporal region, and in one patient w ith exclusively unilateral frontopolar discharges. Conclusions: Interi ctal discharges that demonstrate a consistent unilateral focal prepond erance over a single region, regardless of location, generally predict seizure origin. If the discharges are exclusive to a single region, t here is a greater than 95% probability that all recorded seizures will originate from the expected region.