Survival differences in rheumatoid arthritis interstitial lung disease and idiopathic pulmonary fibrosis may be explained by delays in presentation: results from multivariate analysis in a monocentric UK study.

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) has a better prognosis compared to idiopathic pulmonary fibrosis (IPF). Recent data suggest that antifibrotics are effective in slowing progression across both groups. Hence, we designed this study to investigate the similarities and differences between these groups of patients. This is a retrospective cohort study examining baseline data, progression and outcomes in patients with RA-ILD and IPF prior to antifibrotic use in the Coventry ILD database. Ethics approval was obtained from the University Hospital Coventry and Warwickshire NHS Trust. Statistical analysis was performed using R software and Cox's proportional hazards technique was used for survival analysis. We identified 131 cases, including 49 patients with IPF, 34 patients with RA-ILD and 48 patients with other forms of idiopathic interstitial pneumonia. At baseline, there were significant differences in the groups with RA-ILD patients being significantly younger (65.7 vs 72.4 years), had preserved lung volumes (FVC 95% vs 84.7%) and higher gas transfer (61.5% vs 48.2%) compared to IPF patients. 5-year survival was better for RA-ILD compared to IPF (87.5% vs 40.4%, p = 0.0042). Univariate analysis revealed gas transfer, FVC, age, sex and phenotype (IPF or RA-ILD) were all significant predictors, but multivariate analysis revealed that gas transfer and age were both significantly associated with prognosis, whereas sex, FVC or phenotype were not significant. This study suggests that the difference between RA-ILD and IPF prognosis may be due to demographics and early diagnosis rather than the diseases behaving differently. This has important management implications.