Variability of epileptiform activity in long-term EEGs with short and long intervals in children with epilepsy

Objective: To evaluate the impact of the time factor on the amount of epileptiform activity in long-term EEG recordings in children with epilepsy. Methods: Ten children with epilepsy of different types underwent three 24 h EEG examinations during two consecutive days and with a monthʹs interval. The number of epileptiform discharges during selected corresponding periods of time was counted. Results: The number of epileptiform discharges on three repeated examination days showed no significant difference (ANOVA P=0.88) as intraindividual increases and decreases on different days counterbalanced each other within the group. However the standard deviations of the relative changes were larger between recordings with a monthʹs interval compared to those for consecutive days (86% and 33%). The mean magnitude of change was 55% between days separated by a month compared to 24% on consecutive days. The difference was non-significant but showed a trend towards larger changes with a longer interval (P=0.07). Conclusions: The variability of epileptiform activity was larger when the interval between recordings was 1 month compared to consecutive days. The magnitude of the relative changes between intervals of 1 and 30 days showed a trend towards a difference although not statistically significant. When evaluating repeated long-term EEGs in relation to therapy in children, these variations should be considered.