Cohort study.The aim of this study was to explore the association between blood spinal cord barrier (BSCB) markers and other factors associated with unfavorable outcome among patients with post-traumatic syringomyelia (PTS) who achieved successful intradural adhesion lysis (IAL).Only approximately half of PTS patients receiving IAL have a favorable outcome.Forty-six consecutive patients with PTS and 19 controls (CTRL) were enrolled. All PTS patients underwent physical and neurological examinations and spinal MRI before and 3-12 months after IAL. All patients underwent myelography before surgery. Blood spinal cord barrier (BSCB) disruption was detected by increased intrathecal/serum concentrations of albumin, IgG, IgA, and IgM. Multivariable analysis was performed with a logistic regression model to identify factors associated with unfavorable outcomes. Receiver operating characteristic (ROC) curves were calculated to investigate the diagnostic value of biomarkers.The ages and general health of the PTS and CTRL groups did not differ significantly. QAlb, IGAQ, IGGQ and IGMQ was significantly higher in PTS patients than in controls (P=0.008, 0.0002, 0.003, 0.002, respectively). The degree of intradural adhesion was significantly higher in the unfavorable outcome group than in favorable outcome group (P<0.0001). QAlb, IgAQ, IGGQ and IGMQ was significantly correlated with clinical status (R=-0.38, P<0.01; R=-0.47, P=0.03; R=-0.56, P=0.01; R=-0.43, P=0.05, respectively). Higher QAlb before surgery (OR=2.66; 95% CI 1.134~6.248) was significantly associated with unfavorable outcome. The ROC curve analysis demonstrated a cutoff for QAlb higher than 10.62 with a specificity of 100% and sensitivity of 96.3%.This study is the first to detect increased permeability and BSCB disruption in PTS patients. QAlb>10.62 were significantly associated with unfavorable clinical outcomes following intradural decompression.Prognostic level III.Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.