After the discovery of new class of autoantibodies against neuronal cell surface antigens or synaptic proteins (NSA), the concept of acute encephalitis has dramatically changed. Encephalitis can be divided into infectious and autoimmune encephalitis (AE). AE may have autoantibodies against intracellular onconeuronal antigens (e.g. Hu, Yo, Ri, CRMP5, Ma2), intracellular synaptic proteins (e.g. amphiphysin, GAD65) or NSA (e.g. NMDAR, AMAPAR, GABAaR, GABAbR, LGI1, Caspr2, DPPX).
Most of the classic paraneoplastic anti–neuronal antibodies are less likely pathogenic but IgG NSA antibodies are more likely pathogenic, and the presence of the NSA antibodies implies that patients may respond to immunotherapy. Although early initiation of immunotherapy is often emphasized in AE, antibody testing is not readily accessible in most situation, thus initiation of immunotherapy may be delayed. In 2016, a practical diagnostic approach to AE was published as a position paper in Lancet Neurology to achieve prompt immunotherapy at 3 levels of evidence for AE (possible, probable, and definite) with several new diagnostic criteria including possible AE, probable AE, probable and definite anti–NMDAR encephalitis, autoimmune limbic encephalitis, ADEM, and Hashimoto encephalopathy.
In this lecture, I focus on recent progress in antibody–mediated encephalitis, stiff–person spectrum disorder, and cryptogenic new–onset refractory status epilepticus (C–NORSE) with development of a clinically–based score that predicts C–NORSE.