Comparative analysis of connective tissue disease-associated interstitial lung disease and interstitial pneumonia with autoimmune features

Objective This retrospective clinical study aimed to examine the similarities and differences between connective tissue disease-associated interstitial lung disease (CTD-ILD) and interstitial pneumonia with autoimmune features (IPAF) and to identify the influencing factors of CTD-ILD, with a goal of early detection and active treatment of the disease. Methods We conducted a retrospective study of 480 patients: 412 with CTD-ILD and 68 with IPAF. Demographic features, clinical characteristics, laboratory indicators, and chest high-resolution computed tomography (HRCT) imaging data were analyzed. Results Compared with the IPAF group, the CTD-ILD group contained more women, and the incidences of joint pain, dry mouth/dry eyes, and Raynaud's phenomenon were higher; erythrocyte sedimentation rate (ESR) and D-dimer levels were higher; red blood cell (RBC) and hemoglobin (Hb) levels were lower; a high rheumatoid factor (RF) titer (> 2 times the normal upper limit) was observed, and anti-cyclic citrullinated peptide antibody (anti-CCP), anti-keratin antibody (AKA), antinuclear antibody (ANA), and anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5) levels were higher. Compared with CTD-ILD patients, IPAF patients were more likely to present initially with respiratory symptoms, with higher rates of fever, cough and expectoration, dyspnea, and Velcro crackles; anti-Ro52 titers were higher; incidences of honeycombing opacity, reticulate opacity, patchy opacity, and pleural thickening were greater. Female sex, a high RF titer (> 2 times the normal upper limit), anti-CCP positivity, ANA positivity, and anti-MDA5 positivity were risk factors for CTD-ILD when the odds ratios were adjusted. Conclusion CTD-ILD and IPAF patients differed in demographic features, clinical characteristics, laboratory indicators, and chest HRCT imaging data. Female sex, a high RF titer (> 2 times the normal upper limit), anti-CCP positivity, ANA positivity, and anti-MDA5 positivity were risk factors for CTD-ILD.