Development of anti-NMDA receptor encephalitis in a patient with multiple sclerosis.

Anti-N-methyl-D-aspartate (anti-NMDA) receptor encephalitis is a rare subtype of autoimmune encephalitis, often presenting with early-onset, disease-specific neuropsychiatric symptoms. This case report describes a female patient with relapsing-remitting multiple sclerosis (RRMS) who developed anti-NMDA receptor encephalitis while receiving disease-modifying treatment. She exhibited neurocognitive symptoms and atypical magnetic resonance findings. Clinical and laboratory findings, including lumbar puncture, confirmed the presence of IgG antibodies against the GluN1 subunit of the NMDA receptor, establishing the diagnosis. First-line therapy with methylprednisolone and plasma exchange proved refractory, and immunoglobulin therapy yielded only a suboptimal response. Rituximab achieved the optimal therapeutic effect; however, therapy was followed by recurrent COVID-19 infection in this previously unvaccinated patient. This report highlights the complexities of diagnosis, differential considerations, therapeutic strategies and the detrimental impact of anti-NMDA receptor encephalitis and RRMS on the patient's quality of life.