Quantifying change in pulmonary function as a prognostic marker in systemic sclerosis-related interstitial lung disease

Objective: Clinically meaningful change in systemic sclerosis (SSc) related interstitial lung (SSc-ILD) disease is unknown. The aim of this study was to quantify change in pulmonary function as a predictor of outcome in SSc-ILD.

Methods: All patients had SSc-ILD defined by HRCT chest. All PFTs during follow-up, including FVC (L), DLCO (ml/min/mmHg) and KCO (DLCO/alveolar volume ratio; DLCO/VA) (ml/min/mmHg/L) were retrieved. The rate of change over the first four years, and percentage change in the first year of follow-up were used in ROC curve analysis to determine the best cut-off points to predict adverse outcome (home oxygen, lung transplantation, or death).

Results: Among 264 patients, there were 49 events (38 deaths, 10 supplemental oxygen, one lung transplant) over a mean (± SD) follow-up of 3.0 (± 1.7) years. The rates of decline over time and percentage change over one year in each of FVC, DLCO and KCO were predictive of adverse outcome. Stable PFTs over four years gave the optimal negative predictive values (NPVs) of 88-96%. The best sensitivity-specificity trade-off was a decline in FVC of 10% and in DLCO and KCO of 15% with NPVs of 92-93%.

Conclusion: The course that SSc-ILD takes is evident within the first 1-4 years of follow up. Patients who have no decline in PFTs over 4 years have better outcomes. A decline within one year in DLCO or KCO of 15% or more is a poor prognostic factor, and identifies patients who should be monitored more closely and considered for therapy.