Abstracts

Rationale: Neuronal surface autoantibody (NSAb) mediated encephalitis is a well recognised syndrome in adults and children. The most commonly found autoantibodies are to the NMDA receptor and VGKC-complex. Seizures are one of the most predominant symptoms both in the presentation of autoimmune encephalitis (AE) and during the illness. Recently NSAbs have also been identified in epilepsy patients without encephalitis. These antibodies are thought to be pathogenic although not yet shown to be epileptogenic. We hypothesised that if the seizure semiology was similar between AE patients and those with epilepsy and positive NSAbs, this may suggest a common pathogenic mechanism. We therefore examined the seizure semiology and EEG features of a NSAb positive paediatric autoimmune encephalitis (AE) cohort. This was then compared to a NSAb positive paediatric epilepsy patient cohort.Methods: For the AE cohort, patients presenting to 5 U.K. tertiary neurology centres with a new onset encephalopathy and seizures with positive NSAbs were studied (n=17) (Hacohen et al .,2012). Their clinical and investigative data were retrospectively reviewed. 10 were positive for NMDAR-Ab and 7 had antibodies to the VGKC-complex. The new-onset epilepsy patients were recruited prospectively as part of the Dutch Study of Childhood Epilepsy (Arts et al., 1999), and retrospectively tested for the presence of NSAbs, blinded to the pre-existing clinical data. 5 were positive for NMDAR-Abs and 7 had VGKC-complex antibodies (n=12).Results: The average age of presentation (8.1yrs) and sex distribution was similar in both groups with a female predominance. Three of the NSAb positive epilepsy patients had status epilepticus compared to none in the AE group. Generalised seizures were the most common type of seizure seen in both groups (82% v 83%). The AE group had more frequent focal dyscognitive seizures (53% v 17%) and focal seizures (29% v 17%).There was one case of epilepsia partialis continua (EPC) in the AE group. The EEG in nearly all of the AE group showed encephalopathic features which were not seen in the paediatric epilepsy patients. Epileptiform discharges were seen 7/17 (41%) AE patients compared to 9/12 (75%) of the epilepsy group. Both groups showed similar rates of resistance to first line therapies. On statistical analysis, no significant differences were seen between the two groups (Fisher s exact test).Conclusions: NSAbs are associated with seizures in paediatric autoimmune encephalitis and epilepsy. It is still unclear why some patients with NSAbs develop seizures alone and others as part of an encephalitic illness with other features such as a movement disorder. In this small study, the seizure semiology between the two presenting groups was not significantly different. Future work will focus on exploring the epileptogenic neuronal changes induced in NSAb-mediated seizures in an animal model.