Introduction: Potential uses of magnetoencephalography (MEG) to help noninvasively identify the epileptogenic zone (EZ) in epilepsy surgery and predict seizure outcome include: i) epileptic spike localization, ii) slow wave lateralization, and iii) measurements of resting-state functional connectivity. This is the first study to evaluate multimodal MEG techniques to aid the presurgical evaluation of patients with intractable focal epilepsy.
Methods: We studied 132 focal epilepsy patients who received MEG followed by resection at our institution (follow-up mean = 3.6 years). Interictal spike mapping was performed using dipole source modelling, and MEG/EEG recordings were evaluated for prominent asymmetric slowing (1-4 Hz). In 61 adults without invasive lesions, functional connectivity maps were generated.
Results: Interictal spikes were modelled in 78% of 132 patients, and among those with successful modelling, MEG findings were concordant/specific to the region of resection in 66% of patients. Whereas 85% of patients with concordant/specific MEG spikes became seizure-free, this outcome was achieved by only 37% of individuals with non-specific or discordant MEG spikes (?2 = 26.4, p < 0.001). Asymmetric large-amplitude slowing was observed on interictal MEG recordings in 16% of 132 patients, and lateralized to the EZ in all but one (95%) patient. MEG was significantly more sensitive for asymmetric slowing than EEG, as lateralized EEG slowing was only present in 52% of individuals with MEG slowing, and none of the patients without MEG slowing had asymmetric EEG slowing (?2 = 63.4, p < 0.001). Finally, patients with increased regional functional connectivity within the resection site were more likely to achieve post-operative seizure freedom (88%) than those with neutral (64% seizure free) or decreased (48% seizure free) connectivity (p < 0.02, chi-square).
Conclusions: Multimodal use of MEG offers a novel and valuable approach for noninvasive localization of the EZ and prediction of seizure outcome in epilepsy surgery.
Patient Care: MEG represents a useful tool for interictal spike localization, examination of lateralized slow wave activity, and functional connectivity mapping in pre-surgical epilepsy patients, given high spatio-temporal resolution and lack of signal deterioration by the skull and scalp. MEG can provide valuable information for surgical planning, and other potential uses for MEG in the evaluation of epilepsy patients warrant further attention.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Understand multiple potential uses of magnetoencephalography (MEG) in presurgical evaluation of epilepsy patients, 2) Understand the strengths and weaknesses of MEG in localizing the epileptogenic zone, and 3) Appreciate the value of MEG in predicting post-operative seizure outcome.