Background/Objective Several studies have identified predictors of relapse in antineutrophil cytoplasmic antibody-associated small-vessel vasculitis. However, the role of smoking as a risk factor of relapse has not been elucidated. Therefore, this study aimed to evaluate whether a history of smoking is a dose-dependent independent risk factor for antineutrophil cytoplasmic antibody-associated small-vessel vasculitis relapse. Methods This multicenter retrospective cohort study included 122 patients with granulomatosis with polyangiitis and microscopic polyangiitis (MPA) from 9 nephrology centers in Japan. Dose-response relationships between cigarette smoking and outcomes were assessed using multivariate Cox proportional hazards models, adjusted for clinically relevant factors. The primary outcome was the time from remission to first relapse. Results During the observation period (median, 41 months; interquartile range, 23-66 months), 118 (95.8%) and 34 (21.7%) patients experienced at least 1 remission and 1 relapse, respectively. A log-rank test showed that smoking was significantly associated with relapse (p = 0.003). Multivariate Cox proportional hazards models found current smoking to be associated with relapse (adjusted hazard ratio, 7.48; 95% confidence interval, 2.73-21.0). An association between the risk of relapse and cumulative pack-years of smoking was also noted (p = 0.004). Smoking, however, was not associated with remission. Conclusions Smoking is a significant and dose-dependent risk factor for relapse of MPA. All patients with MPA who smoke should be encouraged to quit.
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