June 27, 2019
A 41-year-old, right-handed man presented with complaints of forgetfulness and altered mentation for 2 months.
ANTI-NMDA RECEPTOR ENCEPHALITIS
- Background
- N-methyl D-aspartate receptor (NMDA receptor or NMDA-R) encephalitis is one of the most common and best characterized subtypes of Autoimmune Encephalitis.
- The NMDA-R is a glutamate receptor and ion channel protein found in nerve cells.
- This subtype is mediated by IgG antibodies against the Glutamate N1 subunit of the neuronal NMDA receptors.
- NMDA-R encephalitis is associated with an underlying ovarian teratoma and ovarian carcinoma in 45% and 23% of women, respectively.
- Clinical Presentation
- Presentation is sub acute to chronic over the span of weeks to months.
- Clinical features are characterized by an initial viral-like prodrome, followed by psychiatric symptoms that includes anxiety, depression, schizophrenia, and psychosis.
- Further progression includes temporal lobe dysfunction (amnesia and seizures) and ultimately culminate in severe neurologic deficits, including autonomic dysfunction, dystonia/dyskinesia, and profound encephalopathy.
- Key Diagnostic Features
- MRI can be normal on initial presentation in about 66%-89% of cases, as opposed to other autoimmune encephalitis.
- Lesions in the hippocampus are the most common abnormal MR imaging finding observed.
- Abnormal FLAIR or T2 hyperintense signals can be seen in the medial temporal lobe, cerebral cortex, basal ganglia, thalamus, and brainstem with or without hippocampal lesions.
- On FDG-PET imaging, hyper-metabolism is seen in mesial temporal lobe structures .
- On ASL perfusion imaging, diffuse increased cerebral blood flow is seen, but is nonspecific for autoimmune encephalitis.
- Differential Diagnosis
- Anti-Hu encephalitis (or other intracellular antigents): Classically paraneoplastic and whole body PET can show primary lesions elsewhere.
- LG1/CASPR2 (former VGKC) encephalitis: Typically presents with dystonia, myotonia, and cognitive decline, among other complaints.
- Systemic Autoimmunity with Encephalopathy: Includes antiphospholipid antibodies and anti-glutamate receptor antibodies.
- Viral encephalitis/syphilitic encephalitis: Will vary depending on the agent and the host immune status, and the diagnosis will be made by PCR or serology.
- Treatment
- Initial treatment is with high-dose steroids and either IVIG(400 mg/kg per day for five days) or plasma exchange in most patients, in addition to tumor removal when appropriate.
- Rituximab and cyclophosphamide are the second-line agents used. Associated with higher percentage of successful outcomes and decreased relapse occurrence.
