Anti-NMDA receptor encephalitis is an autoimmune disorder that affects people of all ages, but predominantly young women (about 50% with an associated ovarian teratoma) and children of both sexes. Patients present with neuropsychiatric manifestations and memory and cognitive deficits and usually progress to catatonia, seizures, autonomic dysfunction, stereotypic movements, and coma. Recovery can be prolonged. The diagnosis can be strongly suspected by history and clinical evaluation and confirmed by detection of CSF IgG antibodies to the GluN1 subunit of the NMDA receptor. Patients often respond to a combination of immunotherapy, including corticosteroids, IVIg or plasma exchange, or rituximab or cyclophosphamide.
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• Anti-NMDA receptor encephalitis is mediated by specific IgG autoantibodies to the GluN1 subunit of the NMDA receptor.
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• Most patients present with neuropsychiatric symptoms that progress to include seizures, movement disorders, autonomic dysfunction, and decreased level of consciousness.
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• The underlying mechanism of the disorder is a reversible antibody-mediated reduction of synaptic NMDA receptors.
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• Almost 80% of patients have full or substantial recovery with early initiation of immunotherapy, and removal of an associated tumor, if present (usually ovarian teratoma), is associated with better outcomes.
Historical note and terminology
In 2005, 4 young women with ovarian teratoma and subacute psychiatric symptoms, seizures, decreased level of consciousness, and frequent central hypoventilation of unknown etiology were reported (47). The patients had inflammatory abnormalities in the cerebrospinal fluid, and all improved after tumor resection, immunotherapy, or both. This supported a paraneoplastic etiology, but some of the teratomas were benign and none of the patients had paraneoplastic (onconeural) antibodies, which target intracellular neuronal antigens (21). Rather, all had an immune response targeting an antigen enriched in the neuropil of the hippocampus that was subsequently identified to be the N-methyl-D-aspartate (NMDA) receptor (14). The response to immunotherapy and the location and function of the NMDA receptor suggested that the disorder, now called anti-NMDA receptor encephalitis, was mediated by the antibodies. Using the presence of the antibodies as a diagnostic test, it soon became clear that this disorder occurs with and without a tumor association and can occur in men (11). It was also shown that similar previously reported cases (some grouped under the term “acute nonherpetic encephalitis of juvenile onset”) were, in fact, cases of anti-NMDA receptor encephalitis (30). The characterization of anti-NMDA receptor encephalitis led to the identification of other encephalitic syndromes, each associated with a specific pathogenic autoantibody that targets neuronal receptors, channels, or synaptic proteins (12). This group of disorders is now often referred to as “antibody-mediated encephalitis” or “autoimmune encephalitis.”