Long-term evaluation of pulmonary function and survival of patients with interstitial pneumonia with autoimmune features

Abstract

Objective Interstitial pneumonia with autoimmune features (IPAF) includes patients with interstitial lung disease with autoimmune features who do not meet criteria for a connective tissue disease (CTD). Previous studies showed a wide variation in the radiologic pattern, pulmonary function and prognosis but there is still limited data on longitudinal outcomes. We aim to describe the long-term pulmonary function, radiological patterns, and survival of IPAF patients and explore a classification based on CTD-like subgroups by using clinical/serologic data. Methods Retrospective analysis of IPAF patients who were sub-classified into six CTD-(like) subgroups: systemic lupus erythematosus-like, rheumatoid arthritis-like, Sjögren’s syndrome-like, scleroderma, myositis-like, and unclassifiable. Linear mixed-effect models were used to compare the change in percent-predicted forced vital capacity (FVC%), percent-predicted diffusion capacity (DLCO%), and six-minute walk distance (SMWD) over time; and survival in the entire cohort and according to CTD-like subgroups and radiological patterns. Results Fifty-nine patients fulfilled IPAF criteria. FVC%, DLCO%, and SMWD remained stable over time. There was no difference between usual interstitial pneumonia (UIP) versus non-UIP radiologic patterns. Thirty-five patients were sub-classified into CTD-like subgroups. Survival decreased from 79% at 60 months to 53% at 120 months in the entire cohort but was similar among CTD-like subgroups and radiological patterns. Conclusion Long-term pulmonary function and six-minute walk test remained stable over 36 months in our IPAF cohort. Prognosis and pulmonary function in UIP had similar outcomes compared to non-UIP. Although 40% of IPAF patients could not be sub-classified, our exploratory subclassification stratified 60% of patients into a CTD-like subgroup.