The value of the systemic immune-inflammation index in assessing disease severity in autoimmune encephalitis.

Background: Autoimmune encephalitis (AE) is a group of autoimmune diseases targeting the central nervous system, characterized by severe clinical symptoms and substantial consumption of medical resources. Neuroinflammation plays a crucial role in disease progression, and detecting inflammatory responses can provide insights into disease status and disease severity. The systemic immune-inflammation index (SII), a novel marker of inflammatory status, has been rarely studied in AE.

Methods: Retrospective analysis of data from AE patients admitted to the First Affiliated Hospital of Zhengzhou University between January 2019 and September 2023 was conducted. Univariate analysis and logistic regression were used to assess the association between SII and patient severity. Nomograms for predicting AE severity were established, and receiver operating characteristic (ROC) curves, concordance index (C-index), calibration curves, and decision curve analysis were employed to evaluate predictive accuracy. Additionally, the Clinical Assessment Scale in Autoimmune Encephalitis (CASE) score was used to assess patient severity.

Results: This study enrolled 157 patients, of whom 57 were classified as severe according to the CASE score. SII, cerebrospinal fluid (CSF) cell counts, disturbance of consciousness, and behavioural abnormalities independently associated with the occurrence of severe cases. The C-index of the nomograms was 0.87, indicating strong association with disease severity, as supported by the calibration. Additionally, SII levels were highest within seven days of onset and decreased after one month. In subgroup analyses of different antibodies, SII also associations with severe cases in NMDAR encephalitis.

Conclusions: Higher SII levels are associated with an increased likelihood of developing severe AE, peaking within 7 days of disease onset and decreasing thereafter, potentially offering a prognostic marker to assess disease progression early in its course.