To explore the value of serial longitudinal EEG as a biomarker to monitor treatment response in autoimmune encephalitis.

There is limited evidence on the management of autoimmune encephalitis, which often presents with first-time seizures and acute encephalopathy. Continuous EEGs are frequently obtained in hospitalized patients with these clinical symptoms to guide treatment decisions. Here, we report a cohort of 17 patients with autoimmune encephalitis with a special emphasis on the longitudinal electrographic changes in relationship to treatment with immunotherapy and anti-seizure medications (ASMs).

We performed a retrospective chart review on patients with autoimmune encephalitis from June 2012 to June 2020 including clinical manifestations, baseline EEG results, anti-neuronal antibody levels and brain MRI findings. We analyzed clinical responses and EEG changes in relation to the timing of administration of ASMs and immunotherapy. The study was approved by the Georgetown University IRB; data was stored in compliance with general data protection regulations.

The 17 patients were diagnosed with the following forms of autoimmune encephalitis: GFAP (1), VGKC/CASPR-2 (1), NMDA (3), VGKC/AMPA+NMDA (1), GQ1b (1), GAD65 (6), MOG (1), checkpoint inhibitor (1), seronegative (2). The most common initial EEG finding was diffuse slowing, followed by focal epileptiform discharges, focal electrographic seizure(s) and normal EEG. Although EEGs demonstrated no significant changes after treatment with ASMs, nine patients had favorable outcomes after treatment with immunotherapy, with EEGs showing early improvement and/or normalization. In eight patients without clinical improvement, EEGs showed persistent slowing and/or epileptiform discharges. Five patients developed refractory seizures. In general, patients with an earlier suspected diagnosis of autoimmune encephalitis with early initiation of immunotherapy had more favorable outcomes.

Immunotherapy appears to be more effective in the management of epilepsy secondary to autoimmune encephalitis when compared to ASMs. EEG should be considered as a biomarker for the earlier identification and treatment of autoimmune encephalitis.