Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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January 14, 2021
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:
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Anti-NMDA antibodies in CSF or blood; CSF is more accurate.
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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.
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Findings on PET/CT are variable and may show hypo- or hypermetabolism in different areas of the brain depending on the phase of disease.
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- 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
