Early Remission of Cerebrospinal Fluid Interleukin‐6 After Initial Immunotherapy Predicts a Good Prognosis in Autoimmune Encephalitis

Background Autoimmune encephalitis therapy requires adjusting the regimen based on therapeutic response; however, clinical indicators of this response remain unknown. Aim To determine the predictive capability of cerebrospinal fluid (CSF), electroencephalography (EEG), and brain magnetic resonance imaging (MRI) in identifying responders to initial treatment for autoimmune encephalitis. Methods We retrospectively selected patients diagnosed with autoimmune encephalitis and treated at our hospital between April 1, 2015, and September 30, 2023. Patients were divided into initial first‐line treatment (FT) responders (those who did not require additional immunotherapy after the initial FT) and initial FT non‐responders (those who required two or more FT sessions or second‐line therapy). CSF, EEG, and brain MRI findings were analyzed before treatment initiation and at the first follow‐up examination. Duration of hospitalization and modified Rankin Scale (mRS) scores were compared between groups. Results Overall, 16 of the 27 selected patients with autoimmune encephalitis were classified as first FT responders, whereas 11 were non‐responders. CSF examination revealed a significantly lower interleukin‐6 (IL‐6) ratio (follow‐up IL‐6/pre‐FT IL‐6) in all responders (IL‐6 ratio < 1). No significant differences were observed between responders and non‐responders in background EEG rhythm frequency, the presence of epileptic discharges, or chronological MRI changes. The length of hospital stay and mRS scores at discharge were significantly lower in the initial FT responder group. Conclusion A lower CSF IL‐6 ratio may be a good predictive marker for response to initial therapy.