Idiopathic Interstitial Pneumonia Associated With Autoantibodies: A Large Case Series Followed Over 1 Year

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.

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]).

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).

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.