Anti-NMDA receptor encephalitis

• Generally, affects younger individuals (95% younger than 45, 37% younger than 18)
• Typically, presentation begins with abnormal behavior (psychosis, delusions, hallucinations, agitation, aggression, or catatonia) with irritability and insomnia
• Over weeks followed by speech dysfunction, dyskinesias, memory deficits, autonomic stability, and decreased level of consciousness.

Patients with relapsing symptoms s/p herpes simplex encephalitis should also be tested for NMDA receptor antibodies, which is an autoimmune reaction affecting 20% of patients with HSE, manifesting as either new onset choreoathetosis or psychiatric symptoms a few weeks after viral infection.

Diagnosis

Diagnostic criteria for probable anti-NMDA receptor encephalitis

1. Rapid onset (<3 months) of at least 4 of the 6 following major groups of symptoms:
   1. Abnormal (psychiatric) behavior or cognitive dysfunction
   2. Speech dysfunction (pressured, verbal reduction, mutism)
   3. Seizures
   4. Movement disorder, dyskinesias, or rigidity/abnormal postures
   5. Decreased level of consciousness
   6. Autonomic dysfunction or central hypoventilation
2. At least one of the following laboratory study results:
   1. Abnormal EEG (focal or diffuse slow or disorganized activity, epileptic activity, or extreme delta brush)
   2. CSF with pleocytosis or oligoclonal bands
3. Reasonable exclusion of other disorders

Diagnosis can also be made in the presence of three of the above groups of symptoms accompanied by a systemic teratoma.

Diagnostic criteria for definite anti-NMDA receptor encephalitis

1. Diagnosis can be made in the presence of one or more of the six major groups of symptoms and IgG anti-GluN1 antibodies (CSF), after reasonable exclusion of other disorders

References

Graus, F. et al. A clinical approach to diagnosis of autoimmune encephalitis. Lancet Neurol. 15, 391–404 (2016). https://pubmed.ncbi.nlm.nih.gov/26906964/