Cerebrospinal fluid YKL‐40 level evolution is associated with autoimmune encephalitis remission

OBJECTIVE: Because of its heterogeneity in clinical presentation and course, predicting autoimmune encephalitis (AIE) evolution remains challenging. Hence, our aim was to explore the correlation of several biomarkers with the clinical course of disease. METHODS: Thirty‐seven cases of AIE were selected retrospectively and divided into active (N = 9), improved (N = 12) and remission (N = 16) AIE according to their disease evolution. Nine proteins were tested in both serum and cerebrospinal fluid (CSF) at diagnosis (T0) and during the follow‐up (T1), in particular activated MMP‐9 (MMP‐9A) and YKL‐40 (or chitinase 3‐like 1). RESULTS: From diagnosis to revaluation, AIE remission was associated with decreased YKL‐40 and MMP‐9A levels in the CSF, and with decreased NfL and NfH levels in the serum. The changes in YKL‐40 concentrations in the CSF were associated with (1) still active AIE when increasing >10% (P‐value = 0.0093); (2) partial improvement or remission when the changes were between +9% and −20% (P‐value = 0.0173); and remission with a reduction > −20% (P‐value = 0.0072; overall difference between the three groups: P‐value = 0.0088). At T1, the CSF YKL‐40 levels were significantly decreased between active and improved as well as improved and remission AIE groups but with no calculable threshold because of patient heterogeneity. CONCLUSION: The concentration of YKL‐40, a cytokine‐like proinflammatory protein produced by glial cells, is correlated in the CSF with the clinical course of AIE. Its introduction as a biomarker may assist in following disease activity and in evaluating therapeutic response.