Abstracts

Rationale:
Delineation of the seizure onset zone (SOZ) is required in children with refractory epilepsy undergoing resective surgery. Electrical source imaging (ESI) is currently used for the non-invasive assessment of SOZ by localizing ictal rhythmic discharges. However, the localization accuracy of ESI performed with other ictal EEG patterns is still under investigation. The goal of this study is to assess the contribution of different ictal EEG patterns to localize the SOZ using ESI with conventional scalp EEG and intracranial EEG in children with refractory epilepsy. We hypothesize that specific ictal EEG patterns can delineate the SOZ more accurately and provide prognostic information prior to surgery.
Method:
We examined 35 children with refractory epilepsy who underwent surgery. We dichotomized surgical outcome into seizure-free and non-seizure-free. We identified ictal onsets recorded with scalp EEG and intracranial EEG. We classified scalp EEG onset as either rhythmic, arrhythmic, paroxysmal fast or repetitive epileptiform discharges; while intracranial EEG onsets as either low-voltage-fast, sharp activity or spike-and-wave. We calculated the distances of scalp and intracranial dipoles from resection (Dres) and compared it between seizure-free and non-seizure-free patients. Mann-Whitney U tests and logistic regression were used to test the association between Dres and outcome among different ictal EEG patterns.
Results:
Twenty-one patients (60%) were seizure free after surgery. A total of 180 scalp EEG seizures (rhythmic activity n=50; arrhythmic activity n=38; paroxysmal fast n=53; repetitive epileptiform discharges n=39) and 177 intracranial EEG seizures (low-voltage-fast n=52; sharp activity < 13 Hz =80; spike-and-wave n=45) were analyzed for all patients. Among scalp EEG ictal patterns, paroxysmal fast, rhythmic activity and repetitive epileptiform discharges presented an association between resection and outcome (p< 0.001; effect size (vda)=0.8; OR[95%C.I.]: 5.3[1.5-22.5] for rhythmic activity; p< 0.005, effect size (vda)=0.75, OR[95%C.I.]: 6.7[1.6-46-6] for paroxysmal fast, and p=0.03, effect size(vda)=0.69, OR[95%C.I.]: 3.42[0.9-14.1] for repetitive epileptiform discharges; Fig. 1).  Among intracranial ictal EEG patterns, low-voltage-fast activity and sharp activity ≤ 13 Hz presented an association between resection and outcome (p=0.03; effect size (vda)=0.69; OR[95%C.I.]: 3.3[1.02-11.3] for low-voltage fast and p< 0.001; effect size(vda)=0.75; OR[95%C.I.]: 3.2[1.3-8-8] for sharp activity ≤ 13 Hz Fig. 2).
Conclusion:
Our results suggest that the use of source imaging to interpret long-term monitoring ictal scalp EEG may offer a boost in the diagnostic armamentarium of several epilepsy centers and should not be limited to ictal rhythmic discharges. Indeed, seizures presenting rhythmic ictal discharges or paroxysmal fast activity at onset should be highly recommended for source imaging of SOZ, as they present the strongest association between resection of SOZ dipoles and seizure freedom after surgery. The use of source imaging to interpret intracranial EEG recorded seizures should also be considered, especially for seizures presenting low-voltage-fast activity and sharp activity ≤ 13 Hz at onset.
Funding:
:R21NS101373-02 (PI: C. Papadelis & S. Stufflebeam) R01NS104116-02 (PI: C. Papadelis)