Abstracts

RATIONALE: Magnetoencephalography (MEG) is accepted as non-invasive and high-resolution method of spike source analysis in partial epilepsy. However, this advantage has been verified mainly in neocortical epilepsies, and little is known about the surgical implications in limbic epilepsies. The purpose of this study is to clarify the clinical significance of MEG on post-operative seizure outcome and residual spiking in surgical treatment of temporal lobe epilepsy (TLE).
METHODS: Interictal scalp electroencephalography (EEG) and MEG were simultaneously recorded for 21 TLE patients both before and 12 months after surgery. Whole-head multi-channels magnetometer (Neuromag Ltd.) was used for MEG recording. Spike sources were estimated on single spike basis for at least 10 spikes a patient. Single equivalent current dipole (ECD) model was fitted for MEG data at the earliest spike peak, and co-registered on the patient[ssquote]s brain MR image. Pre-operative spike dipole localization was compared with seizure outcome and post-operative spike localization.
RESULTS: In pre-operative MEG, sufficient spike samples were obtained from 16 patients. All the spikes were lateralized to the surgically treated side. Post-operative residual spikes were found in 3 of the 16 patients. For 11 patients without neocortical structural lesion, spike localization was classified into two groups: anterior temporal (AT) (n=5) and non-AT localization (n=6). All the patients with AT localization became seizure free (grade I, according to Engel[scquote]s classification) and spike free after anterior temporal lobectomy (ATL). In 6 non-AT patients, 2 became seizure free and spike free; 2 became seizure free with residual spikes; 1 had residual seizures (grade II) but no spikes; and 1 had both residual seizures (grade III) and spikes. Corresponding to the pre-operative localization, all residual spikes were localized in non-AT area. In 5 patients with neocortical structural lesion, MEG spikes were localized near the lesion. All patients became seizure free and spike free after lesionectomy except one patient with multiple lesions (grade II).
CONCLUSIONS: Favorable seizure outcome can be expected by peri-lesional and AT spikes in TLE with/without neocortical lesion. In contrast, non-AT spikes in patients without neocortical lesion can be either remote propagation from medial temporal structures, or non-medial epileptogenicity. Thus, patients with non-AT spikes better undergo intensive evaluations, such as intracranial EEG, for excellent seizure outcome.
Support: Grant-in-Aid for the Development of Innovative Technology No. 12208 from the Ministry of Education, Culture, Sports, Science and Technology of Japan.