Abstracts

Rationale:
Epileptic seizures may be induced by cortical electrical stimulation during stereo-electroencephalography (SEEG). These seizures can further aid delineation of the epileptogenic zone (EZ). However, current knowledge about the concordance between spontaneous and stimulation-induced seizures is sparse. Aim was to quantitatively determine electrical concordance between spontaneous and stimulation-induced seizures in order to improve understanding of the diagnostic value of stimulation-induced seizures and the relation to postsurgical seizure outcome.
Method:
We included 39 consecutive SEEG registrations from 36 patients performed between June 2015 and May 2020 with at least one spontaneous and one stimulation-induced electroclinical seizure. Spectral decomposition was performed on SEEG signals of the recorded seizures for the complete seizure period. Ictal increases and decreases of SEEG power compared to a baseline period were calculated for all contacts in various frequency bands. Pearson correlation coefficients were obtained between spontaneous seizures mutually and between spontaneous and stimulation-induced seizures. We tested whether stimulation in- or outside the clinically defined seizure-onset zone (SOZ) yields seizures with higher correlation to spontaneous seizures and if concordance was associated with postsurgical (radiofrequency thermocoagulation and/or resective surgery) seizure outcome. The study protocol was reviewed and approved by the local independent ethical standards committee.
Results:
Spontaneous seizures (N= 721) showed good concordance per registration (median [Q1-Q3] of 0.68 [0.57-0.85]) and concordance was similar between outcome groups. Stimulation-induced seizures (N= 120) with high electrical concordance ( > 0.7) to spontaneous seizures could be elicited in 67% of the study population (median correlation 0.70 [0.43-0.87]). Concordance for stimulation in- or outside the spontaneous SOZ was similar. Maximal concordance per SEEG was not significantly different in the good (ILAE outcome class 1-2, N= 13) compared to the poor (ILAE outcome class > 2, N= 17) outcome group for stimulation inside the spontaneous SOZ (median 0.66 vs. 0.88, p= 0.16), but was significantly lower in the good compared to the poor outcome group for stimulation outside (0.30 vs. 0.88, p< 0.01) the spontaneous SOZ. In receiver operating characteristic (ROC) analysis, highly correlated seizures stimulated outside spontaneous SOZ proved to be predictive for poor outcome (area under curve (AUC) up to 0.86, CI 95%; 0.71-0.97).
Conclusion:
Stimulation-induced seizures with high electrical concordance to spontaneous seizures can be elicited. Highly concordant seizures resulting from stimulation outside spontaneous SOZ were associated with poor outcome. Findings suggest that seizure-inducing contacts of high concordance stimulation-induced seizures, although outside the clinically defined spontaneous SOZ, may be part of EZ.
Funding:
:None.