Abstracts

Rationale: We explored the likelihood of finding bilateral independent temporal lobe epilepsy (BiTLE) on intracranial EEG (IEEG) in patients whose scalp EEG demonstrated undetermined or bilateral independent temporal seizure onset.Methods: A systematic review was performed searching Embase and Medline up to May 31, 2012, using headings and keywords related to bilateral temporal lobe epilepsy, EEG, surgery and seizure outcome. Studies in all languages, exploring seizure outcome (>1 year follow-up) in patients with BiTLE who underwent IEEG were included. Two reviewers abstracted data independently. We performed two separate analyses among patients whose scalp EEG found bitemporal or ambiguous seizure onsets: 1) patients in whom IEEG demonstrated bilateral seizure onset and underwent surgery. 2) patients whose IEEG demonstrated unilateral onset and underwent surgery. Seizure outcome was categorized as Engel I-II (good outcome) or Engel III-IV (poor outcome). Results: Ninety-nine potentially eligible studies were reviewed in full text, with 13 of these contributing to the 1st analysis, and 35 to the 2nd analysis. Some articles contributed to more than one analysis. In the 1st analysis, out of 1513 patients with undetermined or BiTLE seizure onset on scalp EEG, only 208 (14%) were proven to have BiTLE on IEEG, of whom165 had a temporal lobe resection, with good outcome in 45%. The MRI data for individual patient was available for 32 patients with unilateral temporal lesion in 13 (11 with good outcome) and bilateral in 3 (two with good outcome). In the 2nd analysis, 1048 (69%) patients had unilateral seizures on IEEG, and 67% of these had a good outcome. The MRI data for individual patient was available for 352 patients. Of 44 patients with a unilateral temporal lobe lesion, 36 (82%) had a good outcome. Of 308 non-lesional patients, 211 (69%) had a good outcome. The remaining 10 patients had bilateral mesial temporal sclerosis and 9 had a good surgical outcome. The remaining 257 (17%) had extratemporal or undetermined seizure focus on IEEG, no surgery or had <1year follow-up.Conclusions: Only 14% of patients whose scalp EEG showed ambiguous or bilateral independent temporal seizure onset were found to have bitemporal epilepsy on IEEG. The majority of patients (71%) were found out to have a unilateral temporal focus. Surgical outcome is better in unilateral TLE, particularly when an MRI lesion is identified.