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    Anti-NMDA Encephalitis

    Neurological, Psychiatric and Behaviour

    Last Updated Mar 09, 2020
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    • First discovered in 2007, anti-NMDA encephalitis is now recognized as the most common non-viral encephalitis. It is an autoimmune encephalitis targeting CNS NMDA receptors which appears predominantly in young females (median age ~20, 80% female) but can appear in any age or sex. About half of women of childbearing age with this diagnosis have an associated ovarian teratoma, the removal of which can alleviate symptoms. Otherwise, early treatment with steroids, IVIG, PLEX and immunotherapy has also been associated with improved outcomes.
    • The classic presentation is subacute onset psychiatric symptoms with non-specific neurological complaints (e.g. movement abnormalities, speech disorder), often with a preceding viral prodrome. Compared to primary psychiatric diagnoses, the onset tends to be more rapid and there are more mixed symptoms (e.g. rapidly fluctuating agitation/catatonia, mania/depression, pressured speech/mutism). Autonomic dysregulation (tachycardia, hyperthermia), seizures, hypoventilation, and loss of consciousness tend to occur later on in the course with a worse prognosis. Anti-NMDA encephalitis patients also tend to have more adverse events (e.g. NMS-like symptoms) with antipsychotics.
    • In the patient with bizarre behavior/mixed psych-neuro complaints that are atypical for a primary psychiatric diagnosis, there is a need to consider workup for this potentially fatal diagnosis before sending the patient to psychiatry.

    Diagnostic Process

    • In the 2019 Lancet Neurology update on anti-NMDA encephalitis, experts determined a probable diagnosis can be made with rapid onset (<3mo) of 4/6 of the following symptoms (3/6 if associated ovarian teratoma):
      • Abnormal behavior or cognitive dysfunction,
      • Speech dysfunction (pressured, mutism),
      • Seizures,
      • Movement disorder, dyskinesia, rigidity, abnormal posturing,
      • Altered LOC,
      • Autonomic dysfunction or central hypoventilation, as well as an abnormal EEG or CSF (pleocytosis/oligoclonal bands), and reasonable exclusion of other diagnoses
    • Definitive diagnosis can only be made with CSF anti-NMDA antibodies (available at the Mitogen Lab in Calgary), with at least 1/6 symptom categories.
    • Retrospective studies have shown that 90% of patients have non-specific EEG abnormalities and 80% have pleocytosis or oligoclonal bands on CSF. In the ED, it may be reasonable to LP patients with late symptoms (e.g. dysautonomia, altered LOC, seizures), who are at greater risk of rapid deterioration and need for admission, for basic CSF studies. Otherwise outpatient EEG and/or neurology follow-up may be acceptable for low-risk patients with atypical psychiatric or non-specific neurological complaints. Definitive testing is unlikely to be beneficial in the ED.

    Quality Of Evidence?


    This is a fairly new diagnosis and all available evidence thus far has been retrospective in nature. Despite the increasing recognition of this diagnosis, there are likely under a thousand patients studied with a confirmed diagnosis of this disease process.


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