Extent of disease on high-resolution computed tomography lung is a predictor of decline and mortality in systemic sclerosis-related interstitial lung disease

Objectives. In a multi-centre study, we sought to determine whether extent of disease on high-resolution CT (HRCT) lung, reported using a simple grading system, is predictive of decline and mortality in SSc-related interstitial lung disease (SSc-ILD), independently of pulmonary function tests (PFTs) and other prognostic variables. Methods. SSc patients with a baseline HRCT performed at the time of ILD diagnosis were identified. All HRCTs and PFTs performed during follow-up were retrieved. Demographic and disease-related data were prospectively collected. HRCTs were graded according to the percentage of lung disease: >20%: extensive; <20%: limited; unclear: indeterminate. Indeterminate HRCTs were converted to limited or extensive using a forced vital capacity threshold of 70%. The composite outcome variable was deterioration (need for home oxygen or lung transplantation), or death. Results. Among 172 patients followed for mean (S.D.) of 3.5 (2.9) years, there were 30 outcome events. In Weibull multivariable hazards regression modelling, baseline HRCT grade was independently predictive of outcome, with an adjusted hazard ratio (aHR) = 3.0, 95% CI 1.2, 7.5 and P = 0.02. In time-varying covariate models (based on 1309 serial PFTs and 353 serial HRCTs in 172 patients), serial diffusing capacity of the lung for carbon monoxide by alveolar volume ratio (ml/min/mmHg/l) (aHR = 0.4; 95% CI 0.3, 0.7; P = 0.001) and forced vital capacity (dl) (aHR = 0.9; 95% CI 0.8, 0.97; P = 0.008), were also strongly predictive of outcome. Conclusion. Extensive disease (>20%) on HRCT at baseline, reported using a semi-quantitative grading system, is associated with a three-fold increased risk of deterioration or death in SSc-ILD, compared with limited disease. Serial PFTs are informative in follow-up of patients.