Data from: Electromagnetic source imaging in presurgical workup of patients with epilepsy: a prospective study

Objective: To determine the diagnostic accuracy and clinical utility of
electromagnetic source imaging (EMSI) in presurgical evaluation of
patients with epilepsy. Methods: We prospectively recorded
magnetoencephalography (MEG) simultaneously with electroencephalography
(EEG) and performed EMSI, comprising electric (ESI), magnetic source
imaging (MSI) and analysis of combined MEG-EEG datasets (cEMSI), using two
different software packages. As reference standard for irritative zone
(IZ) and seizure onset zone (SOZ) we used intracranial recordings and for
localization accuracy, outcome one year after operation. Results: We
included 141 consecutive patients. EMSI showed localized epileptiform
discharges (ED) in 94 patients (67%). Most of the ED-clusters (72%) were
identified by both modalities, 15% only by EEG and 14% only by MEG.
Agreement was substantial between inverse solutions and moderate between
software packages. EMSI provided new information that changed the
management plan in 34% of the patients, and these changes were useful in
80%. Depending on the method, EMSI had a concordance of 53-89% with IZ and
35%-73% with SOZ. Localization accuracy of EMSI was between 44% and 57%,
which was not significantly different from MRI (49-76%) and PET (54-85%).
cEMSI achieved significantly higher odds ratio compared to ESI and MSI.
Conclusions: EMSI has accuracy similar to established imaging methods and
provides clinically useful, new information in 34% of the patients.
Classification of Evidence: This study provides Class IV evidence that
EMSI had a concordance of 53-89% and 35%-73% (depending on analysis) for
the localization of epilepsy as compared with intracranial recordings - IZ
zone and SOZ respectively.