Abstracts

Rationale: Occipital Intermittent Rhythmic Delta Activity (OIRDA) is reportedly seen in 13% of the initial EEGs in children with childhood absence epilepsy (CAE). To test the hypothesis that OIRDA in CAE is an epileptiform pattern, which will resolve like 3Hz spike-wave discharges with effective treatment, we assessed the presence of OIRDA on pre- and post-treatment EEGs in children with CAE, enrolled in a randomized clinical trial. Methods: Eligibility, Location and Recruitment: A total of 453 children with newly diagnosed childhood absence epilepsy were enrolled in the parent study and were randomly assigned to treatment with Ethosuximide, Valproic acid or Lamotrigine. EEG: All subjects had a standardized pre-treatment 1-hour, awake video EEG with at least one burst of bilateral synchronous, symmetric spike wave activity (2.7 to 5 Hz), lasting 3 seconds or more, superimposed on a normal background. Follow-up EEGs were obtained at pre-determined time point, typically at 16 weeks after treatment initiation. Both pre- and post- treatment EEGs included at least one trial of hyperventilation. OIRDA was defined as fairly regular or approximately sinusoidal waves, occurring in bursts at 2-3 Hz over the occipital areas unilaterally or bilaterally. Statistical analysis: The primary outcome was presence of OIRDA in post-treatment EEG with or without seizure discharges. The relation between OIRDA and 3Hz spike-wave discharge was tested by appropriate statistical tests, including Pearson's chi square test and Fisher's exact test, analysis of variance (ANOVA), or student's t-test. The significance level will be set at 0.05 (two sided). All analyses were undertaken with STATA for Windows (StataCorp 2007). Results: OIRDA was present in 31 subjects (6.8%) on pre-treatment EEG, of whom 27 had adequate EEGs for analysis. Four subjects left the study prior to any post-treatment EEG and 1 EEG could not be reviewed for technical reason. Of the remaining 22, 18 (82%) were seizure free on post-treatment EEG and 12(67%) of these no longer had OIRDA on the post treatment EEG. There was no significant correlation between the presence/absence of OIRDA and presence/absence of seizures on post-treatment EEG (p=0.5). Conclusions: Overall frequency of OIRDA was 6.8% which is half of the previously quoted rate. In the majority of cases OIRDA disappeared after successful treatment of the spike wave discharges. However, the small number of subjects does not allow for definitive statements whether OIRDA is an epileptiform pattern, or whether its presence at pre-treatment EEG is a predictor of outcome.