Monitoring Brain Activity with EEG Source Localization in Rituximab-Treated Anti-NMDAR Encephalitis: A Case Study.

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a severe autoimmune encephalitis that often demonstrates a favorable response to immunotherapy, including rituximab. While disease outcomes have been widely documented, longitudinal characterization of brain activity changes following treatment remains limited. Electroencephalography (EEG) source localization provides a non-invasive approach for assessing regional brain dynamics. We report a case of a 17-year-old male patient with anti-NMDAR encephalitis who underwent serial EEG recordings before and after rituximab administration, with source power spectral density analysis performed. Symptom improvement following rituximab corresponded with reductions in cortical and subcortical delta power alongside increases in cortical alpha power, while transient symptom exacerbation was associated with elevated delta and diminished alpha activity in the cortex. Cerebellar activity alterations were not observed alongside symptom variations. Moreover, pre-treatment EEG revealed extensive delta band activity in the right hemisphere, with right-sided hypermetabolism observed on 18F-FDG PET/CT. These findings underscore the potential of source-localized EEG as a promising tool for region-specific monitoring of brain activity in NMDAR encephalitis, warranting rigorous validation in larger patient cohorts.