Association Between Serum Syndecan-1 Levels and Relapse in Patients With Antineutrophil Cytoplasmic Antibody-associated Vasculitis: A Medical Record–based Cohort Study in Japan

Background/Objectives: Despite previous reports on the risk factors for relapse in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV), none have evaluated the relationship between serum syndecan-1 levels and AAV relapse. Therefore, this study aimed to investigate the association between serum syndecan-1 levels at AAV diagnosis and subsequent relapses in patients with AAV, hypothesizing that higher levels would be associated with increased risk of relapse. Methods: This single-center, medical record–based cohort study included 60 consecutive patients with microscopic polyangiitis or granulomatosis with polyangiitis treated at Aichi Medical University Hospital in Japan in 2018-2022. The relationship between serum syndecan-1 levels at diagnosis and subsequent first relapse was assessed using multivariable Cox proportional hazards models after adjusting for age, sex, estimated glomerular filtration rate, antineutrophil cytoplasmic antibody (ANCA) titers, Birmingham Vasculitis Activity Score, and AAV classification. The cumulative probability of relapse was calculated using the Kaplan-Meier method and log-rank test. Statistical significance was set at p <0.05. Results: During a median follow-up period of 48 (range, 24 to 64) months, 20 (33.3%) patients experienced at least one relapse. Patients with high-serum syndecan-1 levels (adjusted hazard ratio=19.0, 95% CI: 1.17-307.8) were associated with an increased risk of relapse compared with those with low serum syndecan-1 levels. Conclusions: Among patients with ANCA-associated vasculitis, high-serum syndecan-1 levels at diagnosis were associated with an increased risk of relapse.