Quantitative Computed Tomography Analysis in Rheumatoid Arthritis-Related Interstitial Lung Disease.

Background: Quantitative chest computed tomography (CT) may be a useful predictor of outcome in rheumatoid arthritis-related interstitial lung disease (RA-ILD).

Research question: What is the utility of deep learning-based lung fibrosis quantitation on CT in assessing disease severity, predicting mortality and identifying progression in RA-ILD?

Study design and methods: CT scans on a primary cohort of 289 and a validation cohort of 50 individuals with RA-ILD were assessed quantitatively by using the data-driven texture analysis (DTA) method. We examined associations between quantitative scores for extent of lung fibrosis and pulmonary function and survival.

Results: DTA fibrosis score at baseline showed moderate negative correlation with forced vital capacity (FVC) percentage predicted (primary cohort rho=-0.55, validation cohort rho= -0.50, p<0.001 for both), and diffusing capacity for carbon monoxide (DLCO) percentage predicted (primary cohort rho=-0.67, validation cohort rho=-0.65, p<0.001 for both). Longitudinal change in DTA fibrosis score was associated with changes in FVC and DLCO in the primary cohort (rho=-0.46 and rho=-0.43, respectively, p<0.001 for both). Cox multivariable models adjusted for potentially influential variables showed that the baseline DTA fibrosis score was significantly associated with mortality risk (primary cohort hazard ratio [HR] 1.04, 95% confidence interval [1.03, 1.05], p<0.001; validation cohort HR 1.06, 95% confidence interval [1.01, 1.11], p=0.026). In the primary cohort increase in DTA fibrosis score on sequential scans was associated with increased risk of mortality (HR 1.04, 95% confidence interval [1.01, 1.06], p=0.003) independent of baseline DTA extent.

Interpretation: In two cohorts of patients with RA-ILD, quantitative assessment of lung fibrosis on CT was associated with worse lung function at baseline and risk of mortality. Increase in DTA-derived lung fibrosis score on sequential scans was associated with subsequent risk of mortality. Quantitative CT should be considered for use as a clinical and research outcome assessment tool in RA-ILD.