Differentiation of Temporal Lobe Epilepsy by Scalp Ictal EEG and Its Correlation with Surgical Outcome

Lee, Sang Ahm; Kwak, Kyu Hwan; Lee, Soon Keum; Kang, Joong Koo

Abstract

PURPOSE: Ebersole and Pacia recently introduced a classification of scalp ictal EEG in temporal lobe epilepsy (TLE). So we investigated whether scalp ictal EEG without sphenoidal electrode can differentiate mesial TLE from neocortical TLE and can be predictive of surgical outcome after temporal lobectomy.
METHODS
A consecutive 77 patients (male 43, female 34) with TLE were included who had temporal lobectomy after the comprehensive presurgical evaluation. The patients with mesial TLE were 59 and those with neocortical TLE 18. The total 358 seizures were analyzed using bipolar and monopolar montage without sphenoidal electrodes. Scalp ictal EEGs were categorized into 3 types based on Ebersole and Pacia's classification and then were evaluated with regard to the differentiation of TLE and its correlation with surgical outcome.
RESULTS
1) Out of the total 77 patients, type 1 pattern was observed in 23 (30%), type 2 in 51 (65%), and type 3 in 3 (5%). The number of patients with mesial TLE were 17 (74%) out of 23 with type 1, 41 (80%) out of 51 with type 2, 1 out of 3 with type 3. Type 1 pattern was relatively specific (74%) but not sensitive (30%) for mesial TLE. Also the lesion location of neocortical TLE with type 1 onset was not limited to medial temporal area. 2) Scalp ictal EEG patterns were significantly correlated with surgical outcome only in the subgroup of mesial TLE (p=0.006) but not in neocortical TLE. Type 1 onset pattern in mesial TLE was associated with favorable outcome comparing to type 2 onset.
CONCLUSIONS
Scalp ictal EEG onset pattern cannot accurately differentiate mesial TLE from neocortical TLE. However, its onset pattern can be predictive of surgical outcome.