Clinical features and outcomes of small airway disease in ANCA‐associated vasculitis

Abstract Background and Objective To clarify the prevalence, features and outcomes of small airway disease (SAD) in a Chinese cohort with antineutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV) related pulmonary involvement. Methods SAD was recorded when the manifestations of either centrilobular nodules or air trapping were observed according to CT scans, except for infection or other airway‐related comorbidities. Baseline and follow‐up data were collected retrospectively. Results Of the 359 newly diagnosed AAV patients with pulmonary involvement, 92 (25.6%) had SAD, including 79 (85.9%) cases of anti‐MPO‐ANCA positive, 9 (9.8%) cases of anti‐PR3‐ANCA positive and 2 (2.2%) cases of double positive. Patients with SAD were more likely to be younger, female, non‐smokers, have more ear–nose–throat (ENT) involvement, and have higher baseline Birmingham Vasculitis Activity Score (BVAS) compared to patients without SAD. Several AAV‐related SAD patients have improved lung function and CT scans after immunosuppressive therapy. Patients with SAD had a better prognosis compared to those without SAD. When dividing all patients into three groups: isolated SAD (only small airway involvements), SAD with other lower airway involvements, and non‐SAD, patients in the SAD with other lower airway involvements group had the highest risk of infection, while patients in the non‐SAD group had the worst long‐term outcomes. Similar results were observed in anti‐MPO‐ANCA positive patients when performing subgroup analyses. Conclusion SAD is a unique manifestation of AAV‐related lung involvement and exhibits distinct clinical features. It is vital to focus on SAD because of its association with prognosis and infection in AAV patients, especially in anti‐MPO‐ANCA positive patients. Moreover, SAD might represent a better response to immunosuppressors.