The Clinical Significance of Interstitial Pneumonia with Autoimmune Features in Cryptogenic Organizing Pneumonia: A Prospective Multicenter Observational Study

<b>Background:</b> There are cases of idiopathic interstitial pneumonias (IIPs) that do not meet the diagnostic criteria for connective tissue disease but have clinical features suggestive of autoimmune process. Interstitial pneumonia with autoimmune features (IPAF) was recently proposed as a research concept for these patients. Although several prospective studies on IPAF have been conducted, its clinical significance in cryptogenic organizing pneumonia (COP) remains unclear. <b>Methods</b>: Patients aged ≥20 years with suspected COP were prospectively enrolled between June 2018 and December 2022. Among the enrolled patients, those diagnosed with COP based on computed tomography (CT) and bronchoalveolar lavage (BAL) findings were compared between the IPAF and non-IPAF groups. <b>Results</b>: A total of 56 patients were enrolled in this study. Of these, 30 were diagnosed with COP and included in the analysis. Clinical and serological features were positive in two and six patients, respectively. Each feature was exclusive, and eight patients (26.7%) were diagnosed with IPAF. There were no differences between the IPAF and non-IPAF groups in terms of clinical features, including BAL findings, laboratory data, CT findings, and clinical course. During the one-year follow-up period, the frequency of COP exacerbation did not differ between the IPAF and non-IPAF groups, and no cases of systemic autoimmune disease or death occurred in either group. <b>Conclusions</b>: The COP characteristics of the IPAF and non-IPAF groups are similar in all aspects, and distinguishing between the two groups may be of little significance.