To investigate the impact of changes in T helper 17 (Th17) cell/interleukin-17A (IL-17A) levels in serum and cerebrospinal fluid (CSF) on the clinical outcomes of patients with anti-N-methyl-D-aspartate receptor (NMDAR) antibody-associated autoimmune encephalitis (AE).

Patients with anti-NMDAR antibody-positive AE admitted to the Neurology Department of the Affiliated Nanjing Brain Hospital of Nanjing Medical University, from October 2013 to January 2020 were enrolled. Clinical data including prodromal symptoms, initial symptoms, main clinical manifestations, electroencephalography (EEG) findings, brain imaging features and treatment methods were collected. Meanwhile, the levels of Th17 cells and IL-17A in serum and CSF were detected at the early stage of disease onset. All enrolled patients were followed up for at least 2 years after disease onset. Clinical sequelae and modified Rankin scale (mRS) scores were assessed. Patients with an mRS score≥2 were defined as the poor prognosis group, while those with a score≤1 were assigned to the good prognosis group. Further analysis was conducted to explore the effect of Th17 cell/IL-17A level changes on patients' clinical outcomes.

A total of 54 patients were included in the study, with 20 cases in the poor prognosis group and 34 cases in the good prognosis group. The levels of IL-17A [72.15 (32.60, 102.15) pg/mL] and anti-NMDAR antibody titer [100.0 (32.0, 1000.0)] in CSF, as well as the levels of IL-17A [190.05 (91.9, 381.20) pg/mL] and anti-NMDAR antibody titer [32.0 (10.0, 1000.0)] in serum of the poor prognosis group were significantly higher than those in the good prognosis group [20.15 (11.93, 61.43) pg/mL, 10.0 (3.2, 32.0), 47.55 (33.88, 101.83) pg/mL, 10.0 (3.2, 32.0)], with statistically significant differences (P<0.05). Among patients in the poor prognosis group, 50% (10/20) had presented with mental and behavioral abnormalities, which was significantly lower than that in the good prognosis group (76.74%, 26/34), the difference was statistically significant (P<0.05). The results of the multivariate Logistic regression analysis showed that elevated serum levels of IL-17A and anti-NMDAR antibody titers at the time of onset were independent risk factors associated with poor clinical prognosis in patients with this type of AE (P<0.05).

Elevated levels of IL-17A in early CSF and serum, as well as increased Th17 cell levels in CSF, may indicate a potential poor prognosis of the anti-NMDAR antibody-associated AE patients. Moreover, higher serum IL-17A levels and anti-NMDAR antibody titers at disease onset are independent predictors of poor prognosis. These indicators are expected to serve as biomarkers for early identification of clinical outcomes in AE.