Controversies in clinical neurophysiology. MEG is superior to EEG in the localization of interictal epileptiform activity: Con

Objective: To assess whether MEG is superior to scalp-EEG in the localization of interictal epileptiform activity and to stress the ‘con’ part in this controversy. Methods: Advantages and disadvantages of the two techniques were systematically reviewed. Results: While MEG and EEG complement each other for the detection of interictal epileptiform discharges, EEG offers the advantage of long-term recording significantly increasing its diagnostic yield which is not feasible with MEG. Localization accuracies of EEG and MEG are comparable once inaccuracies for the solution of the forward problem are eliminated. MEG may be more sensitive for the detection of neocortical spike sources. EEG and MEG source localizations show comparable agreement with invasive electrical recordings, can clarify the spatial relationship between the irritative zone and structural lesions, guide the placement of invasive electrodes and attribute epileptic activity to lobar subcompartments in temporal lobe epilepsy and to a lesser extent in extratemporal epilepsy. Conclusions: A clear superiority of MEG over EEG for the localization of interictal epileptiform activity cannot be derived from the studies presently available. Significance: The combination of EEG and MEG provides information for the localization of interictal epileptiform activity which cannot be obtained with either technique alone.