Objectives

The clinical characteristics of interstitial pneumonia with autoimmune features (IPAF) and connective tissue disease interstitial lung disease (CTD-ILD) have not been adequately compared. We compared the clinical characteristics of these two conditions and analyzed the changes in lung function before and after treatment of IPAF.

Methods

A total of 412 patients were enrolled in the study, and their clinical characteristics were assessed. The treatment-related changes in 12 cases of IPAF were analyzed.

Results

Complete clinical data were available for 126 patients with CTD-ILD and 147 with IPAF. All IPAF patients showed autoantibody positivity. The proportion of patients showing extrapulmonary symptoms in the CTD-ILD group was higher than that in the IPAF group (P < 0.05). Patients with IPAF demonstrated lower P(A-a)O₂ and higher PaO₂ and PaCO₂ than those with CTD-ILD (P < 0.05 for all comparisons). Forced vital capacity (FVC) and diffusing capacity of the lungs for carbon monoxide (D_LCO) in IPAF patients were higher than those in CTD-ILD patients (P = 0.023 for FVC; P = 0.011 for D_LCO). Among patients with IPAF, only the proportions of honeycombing and nodules were lower than those in CTD-ILD patients (P < 0.05). Both FVC and D_LCO values increased after treatment in patients with IPAF (P < 0.05).

Conclusion

IPAF showed autoantibody positivity and similar computed tomography (CT) findings as CTD-ILD, and lung function in patients with IPAF improved after immunosuppressive treatment, indicating that IPAF should receive attention and early immunosuppressive treatment like CTD-ILD, even though IPAF exhibits no extrapulmonary symptoms.