Interstitial Lung Disease in ANCA ‐Associated Vasculitis: A European Multicentre Study

Background Interstitial Lung Disease (ILD) can occur in association with ANCA‐associated Vasculitis (AAV‐ILD) or as an isolated entity with positive ANCA (ANCA‐ILD). However, data on the epidemiology and outcomes of these conditions remain limited. Methods A European multicentre retrospective study encompassed patients with AAV‐ILD or ANCA‐ILD. Baseline and subsequent chest CT studies were centrally reviewed. Primary outcomes included forced vital capacity (FVC) decline, respiratory failure, and mortality. Results 162 patients (MPO‐ANCA 85%); 123 (76%) had AAV‐ILD and 39 (24%) ANCA‐ILD. At baseline, Usual Interstitial Pneumonia (UIP) was the most frequent radiologic pattern (57%), while half had a radiological fibrosis grade >10%. Kidney involvement was present in 73%, most commonly Berden focal class. UIP and Non‐specific interstitial pneumonia (NSIP) patterns showed greater annual FVC decline than other patterns (UIP: −1.99%, NSIP: −3.76%, p=0.35 others: +0.36%). An adjusted mixed‐effects model indicated that rituximab was associated with mean FVC % improvement at 12 months (+6.02%; p=0.07). Radiologic progression occurred in ~50%, mainly in younger patients with higher fibrosis severity grade. Respiratory failure (19%) was associated with fibrosis severity (grade 4: HR 4.7; p=0.029) and baseline FVC% (HR 0.95; p=0.002). Over a median 4.2‐year follow‐up, 48% died. Age (HR 1.08; p=0.04) and baseline FVC% (HR 0.97; p=0.05) were independent predictors of mortality. Conclusion At baseline, higher fibrosis severity, UIP, and lower FVC% were associated with worse outcomes. Immunosuppressives, such as rituximab, may help preserve lung function. The need for early identification and individualized treatment in ILD associated with AAV or ANCA is underscored.