LAUSR

Background Some patients with autoimmune characteristics and idiopathic interstitial pneumonia, particularly usual interstitial pneumonia (UIP), do not fit neatly into the category of connective tissue disease‐associated interstitial lung disease (CTD‐ILD), idiopathic pulmonary fibrosis (IPF), or recently proposed yet to be validated criteria for interstitial pneumonia with autoimmune features (IPAF). Outcomes of these patients are unknown. Methods This was a retrospective single‐center study. Analyses of variance compared differences in mean change in FVC and diffusion capacity (Dlco) over 1 year among 124 well‐defined patients (20 patients with positive autoantibodies with or without symptoms of connective tissue disease [AI‐ILD], 15 patients with IPAF, 36 patients with CTD‐ILD, and 53 patients with IPF with negative CTD serologies [Lone‐IPF]). Results Of the patients, 75% with AI‐ILD, 33% with IPAF, and 33% with CTD‐ILD had UIP. Initial FVC and Dlco were similarly moderately reduced across groups. Mean change in FVC over 12 months was as follows: −60 mL (IPAF), −110 mL (AI‐ILD), −10 mL (CTD‐ILD), and −90 mL (Lone‐IPF) (P = .52). Mean change in Dlco was as follows: 2.39 mL/mm Hg/min (IPAF), −1.15 mL/mm Hg/min (AI‐ILD), −0.27 mL/mm Hg/min (CTD‐ILD), and −1.05 mL/mm Hg/min (Lone‐IPF) (P < .001). By pattern of disease, the mean change in FVC was as follows: −140 mL (UIP), 10 mL (nonspecific interstitial pneumonia), and 12 mL (unclassifiable/other) (P = .001). Conclusions No clinically significant differences in pulmonary function to distinguish between patients with AI‐ILD, IPAF, CTD‐ILD, and Lone‐IPF were observed after 1 year. Longer periods of follow‐up are needed to understand the outcomes of these patients. It is not yet clear whether AI‐ILD is a distinct phenotype or a variant of the newly proposed entity IPAF.