Diagnostic Value of Cerebrospinal Fluid Antisuprabasin Antibody in Neuropsychiatric Systemic Lupus Erythematosus

Background Diagnostic attribution of neuropsychiatric symptoms in SLE (NPSLE) remains challenging. This study evaluated whether cerebrospinal fluid (CSF) antisuprabasin (SBSN) antibody can serve as a diagnostic biomarker for NPSLE.Methods In this single-centre, prospective cohort study, patients with SLE presenting with new-onset neuropsychiatric or neurological symptoms were screened between January 2022 and October 2025. Final diagnoses were adjudicated by an independent committee blinded to CSF anti-SBSN antibody results. Patients were classified as NPSLE, SLE with central nervous system infection (SLE-CNSI) or SLE without NPSLE or CNS infection (SLE-Other). CSF anti-SBSN antibody levels were measured by ELISA. Diagnostic performance was assessed for identifying NPSLE against a combined non-NPSLE comparator group comprising SLE-CNSI and SLE-Other.Results Among 190 screened patients, 148 were included in the final analysis, including 48 with NPSLE, 59 with SLE-CNSI and 41 with SLE-Other. CSF anti-SBSN antibody levels showed a stepwise increase across groups, with median concentrations of 47.60 ng/mL in SLE-Other, 72.82 ng/mL in SLE-CNSI and 88.94 ng/mL in NPSLE; all pairwise comparisons were significant (all p<0.001). For identifying NPSLE versus non-NPSLE comparators, CSF anti-SBSN antibody achieved an area under the receiver operating characteristic curve (AUROC) of 0.830, with a sensitivity of 0.812 and specificity of 0.740 at the optimal cut-off of 76.36 ng/mL. CSF anti-SBSN antibody had a higher AUROC than CSF white blood cell count (0.830 vs 0.743; p=0.041) and serum antiribosomal P antibody (0.830 vs 0.665; p=0.003). The three-marker model further increased the AUROC to 0.892 and significantly outperformed CSF anti-SBSN antibody alone (p=0.009).Conclusion CSF anti-SBSN antibody was significantly elevated in NPSLE and demonstrated good diagnostic performance for identifying NPSLE among patients with SLE presenting with neuropsychiatric symptoms. These findings support CSF anti-SBSN as a promising candidate diagnostic biomarker for NPSLE, particularly when combined with conventional CSF inflammatory and serological markers.