THE LATERALIZING VALUE OF SCALP ICTAL EEG PATTERNS IN TEMPORAL-LOBE EPILEPSY WITH UNILATERAL HIPPOCAMPAL ATROPHY WITH SPECIAL ATTENTION TO THE INITIAL SLOW WAVES

We investigated the ictal scalp electroencephalogram (EEG) in 81 seizu res of 25 patients with magnetic resonance imaging (MRI) evidence of u nilateral hippocampal atrophy. All patients had proven temporal lobe e pilepsy because they became seizure free or had only auras after tempo ral lobectomy with a minimum follow-up of 1 year. We studied the initi al 10 seconds of the ictal discharge as an epoch. In addition to the c ommonly encountered recruiting theta rhythm (i.e., increase pattern), we found another dominant ictal pattern at onset (PAO), a decrease pat tern. Decrease pattern, characterized by gradually diminishing high vo ltage slow waves, was the most frequently encountered PAO (44%) and, w hen lateralized, was as accurate as rhythmic theta waves in correlatin g with the side of surgery (97% decrease pattern and 98% rhythmic thet a waves). Lateralized postictal EEG abnormalities were very unreliable in lateralization. Invasive EEG monitoring is not necessary for some patients with temporal lobe epilepsy (TLE) and unilateral hippocampal atrophy even if they show initial slow waves in the ictal EEG pattern. (C) 1997 by Elsevier Science Inc. All rights reserved.