Spatiotemporal mapping of interictal epileptiform discharges in human absence epilepsy: A MEG study

Abstract

a b s t r a c tPurpose: Although absence epilepsy is considered to be a prototypic type of generalized epilepsy, it is still under debate whether generalized 3 Hz spike-and-wave discharges (SWDs) might have a cortical focal origin. Here it is investigated whether focal interictal epileptiform discharges (IEDs), which typically occur in the electro-(EEG) and magnetoencephalogram (MEG) in case of focal epilepsy, are present in the MEG of children with absence epilepsy. Next, the location of the sources of the IEDs is established, and it is investigated whether the location is concordant to the earlier established focal cortical regions involved in the generalized SWDs of these children. Methods: Whole head MEG recordings of seven children with absence epilepsy were reviewed with respect to the presence of IEDs (spikes and sharp waves). These IEDs were grouped into distinct clusters, in which each contribution to a cluster yields a comparable magnetic field distribution. Source localization was then performed onto the average signal of each cluster using an equivalent current dipole model and a realistic head model of the cortical surface. Results: IEDs were detected in 6 out of 7 patients. Source reconstruction indicated most often frontal, central or parietal origins of the IED in either the left and or right hemisphere. Spatiotemporal assessment of the IEDs indicated a stable location of the averages of these discharges, indicating a single underlying cortical source. Discussion: The outcome of this pilot study shows that MEG is well suited for the detection of IEDs and suggests that their estimated sources coincide rather well with the cortical regions involved during the spikes of the SWDs. It is discussed whether the presence of IEDs, classically seen as a marker of focal epilepsies, indicate that absence epilepsy should be considered as a focal type of epilepsy, in which changes in the network are evolving rapidly.

Generalized nonmotor (absence) seizures—What do absence, generalized, and nonmotor mean?

“…[38][39][40] Constant initial unilateral frontal spikes at the onset of absences clearly support the cortical focus theory of bilateral 3/s SWDs. [43][44][45] Furthermore, Sakurai et al 45 showed that cortical regions that constitute a default mode network are strongly involved in the generalized spike wave process in some patients with juvenile absence epilepsy (JAE). [43][44][45] Furthermore, Sakurai et al 45 showed that cortical regions that constitute a default mode network are strongly involved in the generalized spike wave process in some patients with juvenile absence epilepsy (JAE).…”

“…30,39,41,42 Focal abnormalities have also been demonstrated using magnetoencephalography (MEG). [43][44][45] Furthermore, Sakurai et al 45 showed that cortical regions that constitute a default mode network are strongly involved in the generalized spike wave process in some patients with juvenile absence epilepsy (JAE). Combined MEG/EEG recordings demonstrated initial involvement of frontal areas, often combined with activity in the periinsular and subcortical/thalamic areas during bilateral spikes discharges.…”

Multifrequency Dynamics of Cortical Neuromagnetic Activity Underlying Seizure Termination in Absence Epilepsy

“…On electroencephalography (EEG), seizures are characterized by a highly recognizable pattern of generalized (bilateral, symmetric, and synchronous) 3-Hz spike and wave discharges (SWDs) ( Kessler and McGinnis, 2019 ). However, an increasing number of studies have found that CAE was more likely to have focal brain origins that were responsible for absence seizures ( Westmijse et al, 2009 ; Kim et al, 2011 ; Tenney et al, 2013 ; Rozendaal et al, 2016 ; Kokkinos et al, 2017 ).…”

Contributions of Magnetoencephalography to Understanding Mechanisms of Generalized Epilepsies: Blurring the Boundary Between Focal and Generalized Epilepsies?

“…Studies published on combined absence epilepsy (CAE and JAE) are illustrated in Table 2 . Rozendaal et al attempted to compare the interictal and ictal periods in absence epilepsy (6CAE and 1JAE) using the SECD model, and source localizations were most often frontal, central, and parietal regions in either left or right hemisphere ( 135 ). The spatiotemporal assessment of the interictal epileptiform discharges (IEDs) indicated a stable localization of the averaged discharges, indicating a single underlying cortical source.…”