Total cerebrospinal fluid IgA as a candidate adjunctive biomarker associated with autoimmune encephalitis: a retrospective case-control study.

Background: Autoimmune encephalitis (AE) is a rare but severe immune-mediated disease of the central nervous system. Early diagnosis remains challenging, and total cerebrospinal fluid (CSF) IgA is a routinely measurable parameter. However, its association with AE and its potential value as a candidate adjunctive biomarker remain unclear. Objective: To investigate whether total CSF IgA is independently associated with AE and to explore its potential as a candidate adjunctive biomarker for identifying AE cases. Methods: We conducted a single-center retrospective case-control study at the Second Affiliated Hospital of Soochow University (January 2010-June 2025), enrolling patients with autoimmune encephalitis and symptomatic controls with non-inflammatory, non-organic neurological disorders. Clinical, laboratory, and neuroimaging data were collected. Logistic regression was used to assess the independent association of total CSF IgA with autoimmune encephalitis and to construct a prediction model. Model performance was evaluated using receiver operating characteristic curves, calibration plots, decision curve analysis, and bootstrap internal validation. Results: A total of 101 patients with AE and 80 controls were included. Total CSF IgA levels were significantly higher in patients with AE than in controls (median 6.03 vs. 1.46 mg/L, Conclusion: Total CSF IgA was independently associated with AE, and a multivariable model combining CSF IgA with routine laboratory parameters showed excellent discrimination and good calibration in distinguishing AE from symptomatic controls. As a rapidly measurable parameter, it shows promise as a candidate adjunctive biomarker. However, its specificity in distinguishing AE from clinical mimics remains uncertain, warranting validation in larger, independent studies.