Abstracts

Rationale: EEG patterns described in anti-NMDAR encephalitis have included focal or hemispheric slowing as well as diffuse rhythmic delta activity and extreme delta brush, which is unique to the disease. Rhythmic discharges and evolution of the abnormalities have been seen, but noted not to correlate with typical seizure semiologies or dyskinesias. The rhythmic nature of the EEG has at times been interpreted as non-convulsive status epilepticus, but accumulation of long-term cEEG data in affected patients suggests otherwise due to the lack of typical epileptic electrographic features preceding the rhythmic activity or changes in amplitude or frequency during prolonged recordings. Methods: We identified three patients, one male and two female, between the ages of 23 and 26, admitted to our institution with anti-NMDA receptor encephalitis. Cumulatively 25 routine and 103 prolonged (generally 24 hour) EEGs were recorded. Results: Patients had clinical seizures early in the course of their disease. Some early EEG patterns and others later in the disease course were reminiscent of patterns associated with non-convulsive status epilepticus. The EEG pattern did not respond to aggressive anti-epileptic measures including multiple anti-epileptic medications, frequent anesthesia with propofol and/or midazolam, and ketogenic diet. Conclusions: While anti-NMDA receptor encephalitis often presents with seizures, the coma and characteristic EEG pattern that follows does not respond to standard treatments for status epilepticus. The EEG pattern in this disease may represent slow neuronal network oscillations that emerge as a result of downregulation of NMDA receptor-mediated synaptic function due to antibody-induced reduction in NMDA surface receptor density or receptor internalization. Further understanding of these EEG patterns and the pathophysiology that produces them may guide symptomatic treatment and has the potential to improve outcomes associated with prolonged sedation. Funding: n/a