Rheumatoid arthritis, quantitative parenchymal lung features and mortality among smokers

Objectives: There have been limited investigations of the prevalence and mortality impact of quantitative CT (QCT) parenchymal lung features in RA. We examined the cross-sectional prevalence and mortality associations of QCT features, comparing RA and non-RA participants.Methods: We identified participants with and without RA in COPDGene, a multicentre cohort study of current or former smokers. Using a k-nearest neighbour quantifier, high resolution CT chest scans were scored for percentage of normal lung, interstitial changes and emphysema. We examined associations between QCT features and RA using multivariable linear regression. After dichotomizing participants at the 75th percentile for each QCT feature among non-RA participants, we investigated mortality associations by RA/non-RA status and quartile 4 vs quartiles 1-3 of QCT features using Cox regression. We assessed for statistical interactions between RA and QCT features.Results: We identified 82 RA cases and 8820 non-RA comparators. In multivariable linear regression, RA was associated with higher percentage of interstitial changes (beta = 1.7 [0.5], P = 0.0008) but not emphysema (beta = 1.3 [1.7], P = 0.44). Participants with RA and >75th percentile of emphysema had significantly higher mortality than non-RA participants (hazard ratio [HR] 5.86; 95% CI: 3.75, 9.13) as well as RA participants (HR 5.56; 95% CI: 2.71, 11.38) with <= 75th percentile of emphysema. There were statistical interactions between RA and emphysema for mortality (multiplicative P = 0.014; attributable proportion 0.53; 95% CI: 0.30, 0.70).Conclusion: Using machine learning-derived QCT data in a cohort of smokers, RA was associated with higher percentage of interstitial changes. The combination of RA and emphysema conferred >5-fold higher mortality.