Plasma Exchange in Pediatric Autoimmune Encephalitis

Inclusion Criteria: * Childern diagnosed as autoimmune encephalitis according to Cellucci et al., 2020; acute/subacute onset (\<3 months) of encephalopathy with at least one of: new focal CNS findings, seizures, CSF pleocytosis, MRI suggestive of encephalitis, and supportive antibody testing when available. * Autoimmune encephalitis cases indicated clinically for PLEX as determined by the treating team (e.g., severe disease, refractory to steroids/IVIG or as part of first-line combination therapy). Exclusion Criteria: * Hemodynamic instability not amenable to plasma exchange. * Severe coagulopathy uncorrectable prior to PLEX (INR \>2 despite correction, platelets \<50,000/µL unless corrected). * Contraindications to central venous access placement. * Enrollment in another interventional trial that would interfere with the outcomes.