OP62 – 2508: Anti-NMDA receptor antibody status in 3 cases of infant choreo-athetotic movement disorder following HSV-1 encephalitis

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Objective Herpes simplex encephalitis (HSE) is the most common single cause of viral encephalitis in children. In some cases, secondary neurological decline occurs within weeks after HSE mimicking early relapse. Symptoms in this phase often include extrapyramidal choreo-athetotic movement disorders. An autoimmune component has long been suspected in these relapses. Aim of this study was to assess whether antibodies against N-methyl-D-aspartate receptors (NMDARs) may be part of this mechanism. Methods We present a case series of 3 pediatric patients treated with immunomodulation and plasmapheresis for choreo-athetotic movement disorder after HSE. Clinical and serological data were evaluated retrospectively. Anti-neuronal antibodies were assessed from frozen serum and CSF samples using tissue-based and cell-based assays. Results Childrens' median age was 8 months (range 6–11; 3 male). The extrapyramidal choreo-athetotic movement disorder developed 15 to 35 days after onset of encephalitis. All three patients were in need of tube feeding because of pharyngeal dyskinesias. Corticosteroids were administered in 2 cases. All patients received intravenous immunoglobulins and plasmapheresis. The treatment with plasmapheresis started 6–16 days after the onset of the movement disorder and was performed 7–9 times in a period of 14–22 days. In two cases a remission was achieved and in one case only a slight symptom relief was noticed. Two out of three patients revealed positive NMDAR antibodies. In one patient antineuronal antibodies were not detectable. Conclusion Increasing reports on NMDAR antibody related symptoms after HSE strengthen the importance of analyzing anti-neuronal antibodies at earliest clinical clues and to treat with immune modulatory agents. Interestingly, one of our patients with extrapyramidal movement disorder was negative for NMDAR Abs in spite of striking clinical similarities with NMDAR positive patients. This finding might either suggest insufficient sensitivity of anti-neuronal antibody screening methods or indicate presence of currently unknown antibodies causing similar clinical presentation.