Abstracts

Rationale: Since prediction of long-term seizure outcome using preoperative diagnostic modalities remains suboptimal in epilepsy surgery, we evaluated whether interictal spike frequency measures obtained from extraoperative subdural electrocorticography (ECoG) recording could predict long-term seizure outcome. Methods: This study included 61 young patients (age: 0.4 - 23.0 years) who underwent extraoperative ECoG recording prior to cortical resection for alleviation of uncontrolled focal seizures. Patient age, frequency of preoperative seizures, neuroimaging findings, ictal and interictal ECoG measures were preoperatively obtained. The seizure outcome was prospectively measured (follow-up period: 2.5 - 6.4 years [mean: 4.6 years]). Univariate and multivariate logistic regression analyses determined how well preoperative demographic and diagnostic measures predicted long-term seizure outcome. Results: Following the initial cortical resection, Engel Class I, II, III and IV were noted in 35, 6, 12 and 7 patients, respectively. One child died due to disseminated intravascular coagulation associated with pseudomonas sepsis two days after surgery. Univariate regression analyses revealed that ‘incomplete removal of seizure onset zone’, ‘higher interictal spike-frequency in the preserved cortex’ and ‘incomplete removal of cortical abnormalities on neuroimaging’ were associated with a greater risk of failing to obtain Class I outcome. Multivariate logistic regression analysis revealed that ‘incomplete removal of seizure onset zone’ was the only independent predictor of failure to obtain Class I outcome. ‘The goodness of regression model fit’ and ‘the predictive ability of regression model’ were greatest in the full regression model incorporating both ictal and interictal measures (R-square: 0.44; Area under the receiver operating characteristic [ROC] curve: 0.81), slightly smaller in the reduced model incorporating ictal but not interictal measures (R-square: 0.40; Area under the ROC curve: 0.79) and further slightly smaller in the reduced model incorporating interictal but not ictal measures (R-square: 0.27; Area under the ROC curve: 0.77). Conclusions: ‘Seizure onset zone’ and ‘interictal spike frequency measures’ on subdural ECoG recording may be both useful to predict the long-term seizure outcome in epilepsy surgery. Yet, the additive clinical impact of ‘interictal spike frequency measures’ to predict long-term surgical outcome may be modest in the presence of ictal ECoG and neuroimaging data.