Application of Magnetoencephalography in Epilepsy Patients with Widespread Spike or Slow‐wave Activity

Abstract

Summary:Purpose: To examine whether magnetoencephalography (MEG) can be used to determine patterns of brain activity underlying widespread paroxysms of epilepsy patients, thereby extending the applicability of MEG to a larger population of epilepsy patients.Methods: We studied two children with symptomatic localization-related epilepsy. Case 1 had widespread spikes in EEG with an operation scar from a resection of a brain tumor; Case 2 had hemispheric slow-wave activity in EEG with sensory auras. MEG was collected with a 204-channel helmet-shaped sensor array. Dynamic statistical parametric maps (dSPMs) were constructed to estimate the cortical distribution of interictal discharges for these patients. Equivalent current dipoles (ECDs) also were calculated for comparison with the results of dSPM.Results: In case 1 with widespread spikes, dSPM presented the major activity at the vicinity of the operation scar in the left frontal lobe at the peak of the spikes, and some activities were detected in the left temporal lobe just before the peak in some spikes. In case 2 with hemispheric slow waves, the most active area was located in the left parietal lobe, and additional activity was seen at the ipsilateral temporal and frontal lobes in dSPM. The source estimates correlated well with the ictal manifestation and interictal single-photon emission computed tomography (SPECT) findings for this patient. In comparison with the results of ECDs, ECDs could not express a prior activity at the left temporal lobe in case 1 and did not model well the MEG data in case 2.Conclusions: We suggest that by means of dSPM, MEG is useful for presurgical evaluation of patients, not only with localized epileptiform activity, but also with widespread spikes or slow waves, because it requires no selections of channels and no time-point selection. Key Words: MEG-Dynamic statistical parametric mapping-Generalized spike-Slow waveEpilepsy.The appropriate diagnosis of the epileptic syndrome based on the international classification of the epilepsies and epileptic syndromes is the most important factor in treatment decisions by the epileptologist (1). Currently, the diagnosis depends mainly on symptomatic and electrophysiologic findings. In this process, the analysis of interictal discharges (IIDs) and ictal discharges (IDs) in the EEG has played one of the most valuable parts. Magnetoencephalography (MEG) is complementary to EEG; the magnetic fields seen with MEG are selectively sensitive to tangentially oriented source current and are less influenced by the differences in conductivities in the head than are the electrical scalp potentials.

Magnetoencephalographic Mapping of Interictal Spike Propagation: A Technical and Clinical Report

“…The data were high-pass filtered at 7 Hz and low-pass filtered at 40 Hz, the standard clinical values used at our institution for searching for spikes and the clinical definition of epileptic activity. 2,3 The first peak of activity was identified in each MEG IID, and the source was estimated with equivalent current dipoles (ECDs) by using a spheric head conductivity model. 4 Twenty-four ECDs met our statistical evaluation criteria (goodness-of-fit Ͼ80%; 100 nAm Ͻ dipole moment Ͻ400 nAm) and were used for further analysis.…”

“…Recently, the dSPM has been reported to be useful in the analysis of epileptic activity. 2,5 In epilepsy diagnosis, dSPM is a method providing dynamic t statistics or F statistics with respect to baseline, which is the interval showing no epileptic activity. Brain spontaneous activity exceeding this baseline, such as an epileptic event, makes the source estimates significant.…”

Magnetoencephalography localizing spike sources of atypical benign partial epilepsy

“…Segments containing abnormal paroxysms were selected manually. Individual spikes were analyzed to localize the spike source per spike using an equivalent current dipole (ECD) model or dynamic statistical parametric mapping (dSPM) [11,12] . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Shiraishi et al, page 11…”

Magnetoencephalography for Pediatric Epilepsy: How We Do It

“…One or 2 language tests are administered via a video screen placed in front of the patient: picture-naming (via the modified Boston Diagnostic Aphasia Examination) and word recall, to evaluate event-related desynchronization (ERD) in the alpha (8 -15 Hz), beta (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and low gamma (25-50 Hz) bands associated with linguistic computation in a 500-ms latency range immediately before the patient's behavioral response. 39 Visual assessment of hemispheric differences in ERD is made for frontal and posterior temporal regions (Broca and Wernicke areas, respectively).…”

“…MEG localization is particularly valuable when an anatomic lesion cannot be found, even on high-field thin-section volumetric brain MR imaging, [20][21][22][23][24] as well as when multifocal or diffuse disease is clinically suggested. 15,16,22,[25][26][27][28][29][30][31] Our experience with MEG in pediatric patients with epilepsy studied at our institution is reviewed. We compare the localization of the IOZ and functional cortex on the basis of traditional evaluation (including clinical seizure features, interictal electroencephalography [EEG], ictal EEG, MR imaging, nuclear imaging, neuropsychological testing, Wada procedure, and functional cortical mapping) with localization on MEG.…”