Long term effects on epileptiform activity with vagus nerve stimulation in children.

Purpose: We report tong-term effects of vagus nerve stimulation (VNS) on epileptiform activity in 15 children, and how these changes are related to activity stage and to clinical effects on seizure reduction, seizure severity (NHS3) and quality of life (QOL). Methods: Initially, and after 3 and 9 months of VNS-treatment, 15 children were investigated with 24 h ambulatory EEG monitoring for spike detection. The number of interictal epiteptiform discharges (IEDs) and the inter spike intervals (ISIs) were analysed during 2 h in the awake state, and 1 h of rapid eye movement (REM)-, spindle- and delta-steep, respectively. Total number and duration of electrographic seizure episodes were also analysed. Results: At 9 months the total number of IEDs was significantly reduced (p = 0.04). There was a tendency of reduction in all activity stages, and significantly so in delta-steep (p = 0.008). Total etectrographic seizure number was significantly reduced in the 24 h EEG at 3 and 9 months (p = 0.03, 0.05). There was a significant concordance in direction of changes in epileptiform activity and etectrographic seizures at 9 months (p = 0.04). Concordance in direction of changes was seen in 9 of 15 children between clinical seizures and IED (p > 0.3), in 10 of 15 children between QOL and IED (p = 0.3) and in 8 of 15 children between NHS3 and IED (p > 0.3). There was no direct correlation between the extent of improvement in these clinical data and the degree of spike reduction. Conclusion: This study shows that VNS reduces IEDs especially in REM and delta steep, as well as the number of electrographic seizures. It also shows a concordance between reduction in IEDs and etectrographic seizures