A large proportion of "encephalitis" is caused by unknown agents. Of late, a new category of disorders, "autoimmune encephalitis," has been described, which present with features similar to viral encephalitides. A well-delineated and common entity among this group is the recently described anti-NMDAR encephalitis (NMDARE). Although this entity was initially described in young women harboring ovarian teratomas, it is now characterised as well in children and men. Approximately 60% of the patients have an underlying tumor, usually an ovarian teratoma. In 40% of the patients, no cause can be found (idiopathic NMDARE). NMDARE typically presents with psychiatric features followed by altered level of consciousness, severe dysautonomia, hyperkinetic movement disorders, seizures and central hypoventilation. Orofacial dyskinesias resulting in lip and tongue mutilation are quite common. Seizures, are common and may be difficult to treat. The disease can be confirmed by serum and cerebrospinal fluid anti-NMDAR antibodies. Titers of these antibodies can also guide response to treatment. Tumor removal is necessary if identified, followed by immunological treatment. Intravenous methylprednisolone and immunoglobulins aim to suppress/modulate immune response while plasma exchange attempts to remove antibodies and other inflammatory cytokines. Rituximab and cyclophosphamide aim to suppress antibody production. Recovery is slow and often with neurological deficits if treatment is delayed. With many distinctive clinical features, a specific antibody that aids diagnosis, and early effective treatment with commonly available drugs leading to good outcomes, NMDARE is a diagnosis that should be considered early in any case of "unexplained encephalitis."
Keywords: Autoimmune encephalopathy; N-methyl D-aspartate receptor encephalitis; autoimmune encephalitis; limbic encephalitis; paraneoplastic encephalitis.