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Anti-NMDA Encephalitis

  • Background:
    • Anti-NMDA encephalitis is an autoimmune encephalitis with antibodies against NMDA receptors, which are mostly found in the postsynaptic dendrites.
    • This may be associated with a mass (eg, ovarian teratoma) or other cancers (eg, lung, thyroid, breast, colon, and neuroblastoma), hence sometimes presenting as a paraneoplastic syndrome. Screening for a primary tumor should be part of the normal work-up. Such an association, however, is more common in adults and not as well established in children.
  • Clinical Presentation:
    • Initially may present with flulike symptoms followed by psychiatric symptoms (eg, anxiety or psychosis)
    • Seizures, autonomic dysfunction, abnormal movements, catatonia, and coma can also be seen with this condition.
    • Some patients may present with fever.
    • Most cases are seen in young adults and children.
    • Women are 4 times more likely to be affected than men.
  • Key Diagnostic Features:
    • Anti-NMDA antibodies in CSF or blood; CSF is more accurate.
    • Recent evidence suggests that MRI is normal in most patients. The most common MRI findings include increased FLAIR/T2 signal abnormality in the limbic system—anterior temporal lobes, hippocampi, insular cortex, cerebral cortex, and less commonly the basal ganglia, brain stem, and cerebellum. May show restricted diffusion in a multifocal cortical distribution. There is usually no abnormal enhancement or hemorrhage; however, cortical or leptomeningeal enhancement can rarely be seen.  
    • Findings on PET/CT are variable and may show hypo- or hypermetabolism in different areas of the brain depending on the phase of disease.
  • Differential Diagnoses:
    • Viral encephalitis, especially herpes virus: may be indistinguishable involving limbic system; can have hemorrhage, whereas anti-NMDA encephalitis is nonhemorrhagic; patients with herpes encephalitis are usually more acutely sick
    • Seizures: bilateral hippocampi, insular cortex, temporal lobes; may have restricted diffusion
    • Multifocal infarcts: vascular distribution of restricted diffusion
    • Acute disseminated encephalomyelitis (ADEM): preferential involvement of white matter; can enhance and rarely be hemorrhagic; more frequent involvement of basal ganglia
  • Treatment:
    • Corticosteroids, intravenous immunoglobulin, plasmapheresis, rituximab, cyclophosphamide
    • Removal of ovarian teratoma or other tumors if present
January 14, 2021

An 11-year-old boy with fever and malaise for several days followed by encephalopathy and generalized seizures. Extensive viral panel including herpes was negative. MRI studies at 3 (A) and 12 (B–E) days after admission are shown below.

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