Autoimmune encephalitis, autoimmune dementias, and autoimmune psychotic disorders.

The various syndromes of autoimmune encephalitis, with an estimated prevalence of 14 per 100,000, although discovered and better defined during the last 15 years, have left an impactful footprint on autoimmune neurology and have been shaping the novel field of autoimmune neuropsychiatry. Many patients presenting with altered mental status and behavioral aberrations of subacute onset and initially treated with antipsychotic medications turn out to have autoimmune conditions caused by autoantibodies against CNS antigens that respond dramatically to immunotherapy. This chapter describes the different clinical syndromes connected to different autoantibodies and discusses general principles of autoimmunity in connection with intracellular or antisynaptic antibodies as well as different aspects of the evolving concept of autoimmune neuropsychiatry. Further, the chapter summarizes evidence of autoantibody pathogenicity and of potential triggers for this kind of autoimmunity including infections, neoplasms, and immune checkpoint inhibitors. Finally, it analyzes therapeutic maneuvers as well as prognosis. Overall, the chapter stresses the paramount importance of early recognition and diagnosis leading to targeted immunotherapy and improved outcomes.