Interictal epileptogenic zone localization in patients with focal epilepsy using electric source imaging and directed functional connectivity from low‐densityEEG

Abstract

Summary Objective Electrical source imaging ( ESI ) is used increasingly to estimate the epileptogenic zone ( EZ ) in patients with epilepsy. Directed functional connectivity ( DFC ) coupled to ESI helps to better characterize epileptic networks, but studies on interictal activity have relied on high‐density recordings. We investigated the accuracy of ESI and DFC for localizing the EZ , based on low‐density clinical electroencephalography (EEG) . Methods We selected patients with the following: (a) focal epilepsy, (b) interictal spikes on standard EEG, (c) either a focal structural lesion concordant with the electroclinical semiology or good postoperative outcome. In 34 patients (20 temporal lobe epilepsy [TLE] , 14 extra‐TLE [ETLE ]), we marked interictal spikes and estimated the cortical activity during each spike in 82 cortical regions using a patient‐specific head model and distributed linear inverse solution. DFC between brain regions was computed using Granger‐causal modeling followed by network topologic measures. The concordance with the presumed EZ at the sublobar level was computed using the epileptogenic lesion or the resected area in postoperative seizure‐free patients. Results ESI, summed outflow, and efficiency were concordant with the presumed EZ in 76% of the patients, whereas the clustering coefficient and betweenness centrality were concordant in 70% of patients. There was no significant difference between ESI and connectivity measures. In all measures, patients with TLE had a significantly higher ( P < 0.05) concordance with the presumed EZ than patients with with ETLE. The brain volume accepted for concordance was significantly larger in TLE . Significance ESI and DFC derived from low‐density EEG can reliably estimate the EZ from interictal spikes. Connectivity measures were not superior to ESI for EZ localization during interictal spikes, but the current validation of the localization of connectivity measure is promising for other applications.

Analysis of Interictal Epileptiform Discharges in Mesial Temporal Lobe Epilepsy Using Quantitative EEG and Neuroimaging

“…Therefore, precise determination of the epileptogenic zone is vital for surgical planning, and the possibility of noninvasive tests being used in the preoperative routine may benefit these patients. Coito et al (29) evaluated IED routine EEG with electrical source analysis in 34 patients (20 temporal lobe epilepsy and 14 extra temporal epilepsy) before and after surgery. The efficiency were concordant with the presumed epileptic zone in 76% of the patients, showing the importance of these findings.…”

Accelerated long‐term forgetting in focal epilepsy: Do interictal spikes during sleep matter?

“…On the other hand, some types of epilepsy are associated with cognitive impairment due to the massive occurrence of interictal spikes during sleep (Landau–Kleffner syndrome, continuous spikes and waves during sleep) 28,44,45 . Interictal discharges have been shown to disturb long‐range brain connectivity 46–48 . The rate of interictal spikes significantly increases during non–rapid eye movement (NREM) sleep, 49,50 mostly in medial temporal regions whether these regions belong to the epileptogenic zone (EZ) or not, 51 thus possibly disrupting sleep‐dependent processes of long‐term memory consolidation.…”

Lateralization of epilepsy using intra‐hemispheric brain networks based on resting‐state MEG data

“…Many studies have investigated a potential application of local graph measures, particularly those that denote the hub status of a node such as betweenness centrality (BC), in localizing the seizure onset and epileptogenic zones of patients with focal epilepsy to improve outcomes after epilepsy surgery. These localization studies have been performed using effective connectivity analysis with ictal and interictal iEEG (Ren et al, ; Wilke, Worrell, & He, ) and FC analysis with interictal EEG (Coito et al, ) and MEG (Juarez‐Martinez et al, ; Nissen et al, ; Nissen et al, ).…”