Abstracts

Rationale: Vagus nerve stimulation (VNS) exerts antiepileptic effect via nucleus of the solitary tract in brainstem (Krahl SE, Clark KB. Vagus nerve stimulation for epilepsy: A review of central mechanisms. Surg Neurol Int. 2012;3:S255-9). No significant difference in VNS efficacy between partial seizures and generalized seizures in adult patients (Wheeler M, et al. Efficacy of vagus nerve stimulation for refractory epilepsy among patient subgroups: a re-analysis using the Engel classification. Seizure. 2011;20:331-5). Epileptic spasms and brief tonic seizures are medically refractory seizures in childhood epilepsy. There have been little investigations for VNS efficacy based on seizure types. We hypothesize that VNS is less effective for epileptic spasms and brief tonic seizures compared to partial seizures and secondary generalized seizures. Methods: We retrospectively collected the medically refractory epilepsy patients who underwent VNS implantation = < 20 year-old. We classified the patients into group A: main seizures are epileptic spasms/brief tonic seizures, and group B: partial seizures/secondary generalized seizures. Epileptic spasms and brief tonic seizures were confirmed on ictal scalp EEG. We used McHugh classification for seizure outcome evaluations. We compared the clinical information and the seizure outcome between the two groups. For the comparison, we used Mann-Whitney U-test. Results: We collected 37 patients (group A: 20; group B: 17). The seizure onset age ranged 0-14 year-old (median 1). The age at implantation ranged 1-19 year-old (12). The follow-up period ranged 1.0-5.3 years (2.7). Twenty-four patients showed severe developmental delay (IQ/DQ: < 30). Group A significantly presented earlier seizure onset (p=0.004), and worse development (p=0.003) than those of group B. The seizure outcome in group A (class I: 2; II: 2; III: 5; IV: 0; V: 11) were significantly poorer than those in group B (I: 4; II: 6; III: 2; IV: 2; V: 3) (p=0.020). Conclusions: VNS demonstrated less effectiveness for epileptic spasms/brief tonic seizures in children than partial seizures/secondary generalized seizures. Younger seizure onset and poor cognitive function may indicate that diffuse brain dysfunction and the extensive epileptic network to provoke epileptic spasms/brief tonic seizure. The efficacy of VNS for partial seizures/secondary generalized seizures in children with later onset seizures and relatively better cognitive function may indicate that VNS works in the patients with local dysfunction and focal epileptic network. Funding: No fundings