Abstracts

Rationale: Magnetoencephalography (MEG) is a non-invasive technique to measure the extracranial magnetic fields generated by intracranial currents. MEG can detect the synchronous activity of populations of neurons, and therefore has been especially useful in the study of epilepsy. MEG has advantages over standard electroencephalography (EEG) as magnetic signals are not distorted by the tissues surrounding the brain. Additionally, MEG typically uses an order of magnitude more sensors to record activity, allowing for more precise source imaging. Currently, a combination of EEG, MEG, invasive electrical monitoring, and imaging is used to evaluate patients with epilepsy. An improved understanding of these techniques would help all of these modalities to work synergistically to provide the best outcome to patients with the least risk and cost. As MEG is less commonly available than other modalities, we describe the use of MEG at Wake Forest Baptist Health in the evaluation of epilepsy.Methods: All patients were identified by a search of computerized records at Wake Forest Baptist Hospital (IRB 15854). Selection criteria included any patient who had a MEG recording for the evaluation of epilepsy from March 2006 through May 2011. The clinical record was checked for EEG, invasive monitoring, structural imaging, and metabolic imaging in the same patients and, if available, such data was collected as well. Clinical outcome was determined by review of notes from clinic appointments.Results: A total of 144 individuals were identified who had an MEG in the course of evaluation for epilepsy. The average age was 28.3 years and 53% were female. Ninety-five adult and 49 pediatric individuals were evaluated by MEG. Sixty-eight percent of MEG runs captured epileptiform activity. A total of 91 of the 144 cases underwent cortical mapping in the MEG (35 language, 23 auditory, 37 motor, 52 somatosensory, 7 visual). Thirty-eight individuals underwent surgery after the MEG. In 52% of cases the MEG data was concordant with EEG and/or invasive monitoring. In 24% of cases the MEG was concordant with a seizure focus identified on functional imaging such as single-photon emission computed tomography (SPECT) and/or positron emission tomography (PET).Conclusions: These findings describe the use of MEG in the evaluation of epilepsy at Wake Forest Baptist from March 2006 through May 2011. These findings describe both the complementary and the unique information that MEG provides. Furthermore, this review demonstrates the feasibility of performing functional mapping using the MEG. This compilation of data provides a basis upon which informed decisions can be made regarding the clinical use of MEG, as well as guiding the design of future retrospective and prospective studies.