Comparison of the clinical characteristics of rheumatoid arthritis patients with and without interstitial lung disease

Abstract

Introduction: The clinical importance of rheumatoid arthritis-associated interstitial lung disease has been increased because the usual interstitial pneumonia (UIP) is the most common subtype of interstitial lung disease (ILD) on high-resolution computed tomography (HRCT) in rheumatoid arthritis (RA)and has poor survival rate compared to other forms of ILD related to connective tissue disease. The clinical characteristics and laboratory data of RA patients with and without ILD were compared in order to clarify the risk factors for ILD in RA patients. Furthermore, risk factors of mortality in the RA patients with ILD group were analyzed. Methods: A total of 77 RA patients with ILD and 231 age/sex-, and disease duration-matched RA patients without ILD who were followed from 1991 to 2011 at Seoul National University Hospital were enrolled in this study. Epidemiologic, clinical, and laboratory information including rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) were obtained through medical chart review. The erythrocyte sedimentation rates (ESR), C-reactive protein (CRP) levels, presence of erosion on joint X-rays, and mean corticosteroid doses were examined in order to compare RA outcomes between the RA patients with and without ILD. Cox proportional hazard models were used to estimate the risk of mortality in the RA patients with ILD. Results: In the RA with ILD group, the titers of the RF and the anti-CCP were significantly higher compared with those in the RA without ILD group (p = 0.001 for both). The RA patients with ILD had higher frequency of a history of tuberculosis or nontuberculous mycobacteria (NTM) (p = 0.022). In addition, the RA with ILD group exhibited higher levels of CRP at the time of RA diagnosis (p = 0.014) and higher ESR (p = 0.022) and CRP levels (p < 0 .001) throughout the 10-year follow-up period. These patients received higher mean daily dose of corticosteroid (p < 0.001). In the subgroup analysis of RA patients with ILD, 28 (36.4%) patients died with the mean follow-up duration of 8.7 years. Male patients, high RF titers and UIP subtype on HRCT had significantly worse survival, and those with nonspecific interstitial pneumonia (NSIP) on HRCT had better survival. In the multivariate analysis, a UIP subtype on HRCT and older age at the time of ILD diagnosis were significantly associated with mortality of RA with ILD. Conclusions: The RA patients with ILD had higher RF and anti-CCP titers and baseline CRP levels compared with those without ILD. A UIP subtype on HRCT and older age at the time of the diagnosis of ILD were significantly associated with mortality of RA with ILD.