Sleep-Related Seizures in Refractory Focal Epilepsy: Electroclinical Findings and Surgical Outcome

Background: Sleep Seizures (SSs) generally occur in refractory focal epilepsy, but their detailed characteristics and circadian patterns are still controversial. The effect of SSs on epilepsy surgery outcome has been addressed in few studies without definitive prognostic value.   Objectives: This study investigated the characteristics of SSs and their prognosis in refractory focal epilepsy. Materials & Methods: This retrospective cross-sectional study was conducted in the referral epilepsy center in Isfahan, Iran from 2011 to 2015. It investigated SSs in patients with refractory focal epilepsy who underwent pre-operative evaluation. Demographic data, electroclinical findings, pathology, and postsurgical outcomes were analyzed and compared to Wake Seizures (WSs).  Before the main analysis, Shapiro-Wilk test of normality was performed. Then the Independent sample t test, Chi-square test, Fisher’s exact test, Mann-Whitney U test and 1-way ANOVA were used to analyze the obtained data in SPSS. All probability tests were two-tailed and the level of significance was defined as P≤0.05. Results: A total of 371 seizures in 113 patients were studied. The sleep/wake seizure ratio in Temporal Lobe Epilepsy (TLE) and Extratemporal Lobe Epilepsy (ETLE) were 0.54 and 0.91, respectively. The peak incidence of SSs in TLE and ETLE were during 4.00 to 8.00 and 0.00 to 4.00, respectively. SSs were considerably associated with EEG changes before clinical signs. Ictal EEG localization was more successful in SSs of extratemporal origin. Based on pathology findings, Focal Cortical Dysplasia (FCD) was highly associated with SSs. Left epileptogenic zone and FCD accompanied a less favorable outcome in SSs. Conclusion: SSs are significantly more frequent in patients with ETLE and follow specific circadian patterns based on epileptogenic zone. Seizure semiology and EEG findings are in favor of more localized onset of epileptic activity in SSs of extratemporal origin. The side of epileptogenic zone, circadian pattern of seizures, well-defined epileptogenic lesion in MRI and pathology, could affect postsurgical outcomes in SSs.