To study the cerebrospinal fluid indices (CSF) and their association with prognosis of AE.

CSF indices reflecting intrathecal antibody production and blood-brain barrier impairment are not routinely assessed in patients with autoimmune encephalitis (AE).

This is a retrospective cohort study conducted in AIMS, a tertiary care research and teaching hospital in South India, Kochi. Our cohort comprised of all adult patients with definite/probable/possible AE admitted from August 2016 till November 2021. We introduced a classification of treatment response based on modified Rankin Scale change over time and treatment modalities. To look into associations between the factors a univariate and then multivariate binary logistic regression was used (for the whole cohort, seronegative cases). A two-tailed Fisher's exact test was used for a small subset of seropositive cases.

In our cohort of 60 patients (six [10%] seropositive cases), a good rapid treatment response associated with cerebrospinal fluid white blood cell count of more than 4 cells/mm³ (OR, 4.57; 95% CI 1.31-15.96; P = .02) and positive immunoglobulin G (IgG) Local Synthesis (OR, 7.27; 95% CI 1.56-33.86; P = .01). Albumin Index had association with a poor Glasgow Coma Scale score at the nadir of the disease (OR, 1.17; 95% CI 1.01-1.34; P = .04). Similar results were yielded in the seronegative cohort. IgG Local Synthesis appeared to be a strong predictor for good rapid treatment response in both univariate and multivariate (adjusted OR, 28.71; 95% CI 2.12-389.22; P= .01) analysis. Time to immunotherapy reversely correlated with good response overall (in the cohort with outliers removed [N=49]: unadjusted OR 0.97, 95% CI 0.95-0.99; P= .01; adjusted OR 0.97; 95% CI 0.95-0.99; P= .008).

CSF indices reflecting intrathecal antibody production and blood-brain barrier impairment appear to be promising predictors of disease severity and therapeutic response in patients with autoimmune encephalitis.