title: Variability of epileptiform activity in long-term EEGs with short and long intervals in children with epilepsy.
abstract: 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 month's 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 month's 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.
authors.affiliation: Department of Pediatrics, Astrid Lindgrens Childrens Hospital, Karolinska Hospital, Stockholm, Sweden. marda@child.ks.se
authors.forename: M
authors.initials: M
authors.lastname: Dahlin
authors.forename: A
authors.initials: A
authors.lastname: Nergårdh
authors.forename: P
authors.initials: P
authors.lastname: Amark
authors.forename: E
authors.initials: E
authors.lastname: Knutsson
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D002648:Child; D002675:Child, Preschool; D004569:Electroencephalography; D004828:Epilepsies, Partial / Q000145:classification / Q000503:physiopathology*; D004829:Epilepsy, Generalized / Q000145:classification / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D013997:Time Factors