Are risk predicting models useful for estimating survival in rheumatoid arthritis-associated interstitial lung disease?

Abstract

Risk predicting models have been applied in idiopathic pulmonary fibrosis (IPF), but not yet validated in patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD). The purpose of this study was to test the suitability of three prediction models as well as individual lung function and demographic factors for estimating prognosis of the RA-ILD patients. Clinical and radiological data of 59 RA-ILD patients was re-assessed. GAP (gender, age, physiologic variables) and the modified interstitial lung disease (ILD)-GAP indexes as well as the composite physiologic index (CPI) were tested for predicting mortality using the goodness-of-fit test and Cox model. Potential predictors of mortality were searched also among single lung function parameters and clinical characteristics. The median survival was 152 months in GAP stage I and 61 months in GAP stage II (p=0.017). Both the GAP model and ILD-GAP model produced accurate estimates of the 1-year, 2-year and 3-year mortality. CPI (p=0.025), GAP (p=0.008) and ILD-GAP (p=0.028) scores, age (p=0.002), baseline diffusion capacity to carbon monoxide (DLCO) (p= 0.014) and hospitalization due to respiratory reasons (p=0.039) were significant predictors of mortality in univariate analysis. The CPI score (HR 1.03, p=0.018) and baseline DLCO (HR 0.97, p=0.011) remained significant predictors of mortality after adjusting for age. We conclude that the GAP and ILD-GAP are applicable in RA-ILD risk estimation in a similar manner than in IPF. Baseline DLCO and CPI score predicted also survival.