Can ictal-MEG obviate the need for phase II monitoring in people with drug-refractory epilepsy? A prospective observational study.

PURPOSE: To determine if ictal-magnetoencephalography (ictal-MEG) source localization (SL) added information towards delineating the ictal-onset zone (IOZ), whether and how it helped final decision-making in epilepsy-surgery.

METHODS: Definite focal clusters on ictal-MEG were available for 32 DRE-patients, data was analyzed (single equivalent current dipole (ECD) model), SL done. Clinical history, long-term video-EEG (VEEG) monitoring, epilepsy-protocol MRI, FDG-PET, ictal-SPECT and interictal-MEG were discussed at the multispeciality Epilepsy Surgery Case-conference (ESC). Cases were reviewed with ictal-MEG SL presented only at the last ESC (after decision using other available modalities). Patients were grouped as VEEG localization and MRI-lesion concordant (Group-A), discordant (Group-B), and no MRI-lesion (Group-C). Final hypothesis or decision, surgical outcome in those operated, and how ictal-MEG data influenced them were recorded.

RESULTS: Five lesion-negative patients had identification of lesions after review of MRI with ictal-MEG SL. The difference between numbers of patients cleared for surgery without and with ictal MEG data was statistically significant (p=0.0044); but the difference in those cleared for phase II monitoring was not (p=1.00). Ictal MEG influenced decisions on possibility of surgery in 9 and converted decisions of phase II monitoring in 11 patients to electrocorticography-guided lesionectomy (20 in all; Group A-11, Group B-4, Group C-5); five were operated, with good seizure-control on follow-up.

CONCLUSIONS: Delineation of IOZ by ictal-MEG helped convert DRE patients unsuitable for surgery or planned for phase II monitoring into candidates suitable for surgery, even ECoG-guided resections, and resulted in favorable outcomes in those who were operated.