Anti-NMDA Receptor Encephalitis and Other Autoimmune and Paraneoplastic Movement Disorders

Abstract

A substantial number of movement disorders are mediated by immunological mechanisms. In some instances, the immune response is triggered by the presence of a tumor that ectopically expresses a neuronal protein, leading to a brain autoimmune response or paraneoplastic syndrome. Other immune-mediated movement disorders may be post-infectious, likely triggered by molecular mimicry or other, as yet unknown, mechanisms. There is an expanding group of syndromes that are associated with antibodies against cell surface or synaptic proteins and may cause early and prominent movement disorders. Anti-NMDA receptor encephalitis is the most frequent of these disorders that may occur with or without tumor association, affect children and adults, and can be severe but responsive to treatment. Recognition of this and other immune responses to synaptic proteins is important because, different from classical paraneoplastic syndromes, they often respond to immunotherapy. Because the presentation and clinical course of immune-mediated syndromes often develop very quickly, and failure to recognize and treat these disorders may lead to morbidity or even mortality, we believe that this qualifies these syndromes as movement disorder emergencies. This chapter is structured in a clinical way, with focus on the predominant movement disorder. Some of the entities do not have specific diagnostic biomarkers and are instead diagnosed based on the “clinico-radiological syndrome,” such as opsoclonus–myoclonus–ataxia syndrome and Sydenham’s chorea.