Background/Purpose:  To characterize a cohort of patients with rheumatoid arthritis (RA) who have interstitial lung disease (ILD) and to assess the utility of the GAP (gender, age, pulmonary function) and ILD-GAP staging system for mortality risk prediction in patients with RA-ILD.

Methods:  All patients with RA and ILD seen at a single center from 1998-2014 were identified and manually screened for study inclusion and followed until death or December 31, 2015. All cases fulfilled the 1987 ACR criteria for RA. Pulmonary function test (PFT) results closest to ILD diagnosis were recorded. The GAP and ILD-GAP scores were calculated using age, sex, and lung physiology variables (forced vital capacity [FVC], diffusing capacity for carbon monoxide [DLCO]) at ILD diagnosis. Survival rates were calculated using the Kaplan-Meier method. Cox models were used to examine associations between baseline characteristics and mortality. The accuracy of risk predictions was assessed using standardized incidence ratios and c-statistics.

Results: Of the 181 included patients, 87 (48%) were female and 96% were Caucasian. The mean age at ILD diagnosis was 67.4 (±9.9) years with a median time of 4.9 (range: -10.9 to 48.1) years from RA to ILD diagnosis. Median follow-up time was 3.1 (range: 0.01 to 14.8) years. Sixty-seven were never smokers (37%) and 44 (24%) had erosive disease. Ninety-eight (54%) had usual interstitial pneumonia (UIP), 73 (40%) had non-specific interstitial pneumonia (NSIP), and 10 (6%) had RA-related organizing pneumonia (OP). Anti-citrullinated protein antibodies were present in 77% of 136 tested and rheumatoid factor in 82% of 176 tested. The baseline PFTs at time of ILD diagnosis included mean percent predicted FVC of 72% ± 20 and DLCO of 56% ±20. At last follow-up 72 had died. Pulmonary disease accounting for 21 (29%) of deaths. The five-year survival rate was 59.7% (95% confidence interval [CI] 51.5-69.2). Survival did not differ between ILD types (p=0.42). Baseline risk factors significantly associated with mortality were age at ILD diagnosis (hazard ratio [HR]: 1.34 per 10 year increase; 95% CI: 1.11-1.63) and RA disease duration at ILD diagnosis (age and sex adjusted HR 1.71 per 10 year increase; 95% CI: 1.22-2.39). Lower baseline percent predicted DLCO and FVC were associated with significantly higher mortality (HR: 2.48; 95% CI: 1.55-3.95 and HR: 1.20; 95% CI: 1.04-1.41, per 10% predicted decrease, respectively). GAP and ILD-GAP scores were calculated for 159 patients with PFTs within 6 months of diagnosis. 30 patients died within 3 years of diagnosis. The GAP model predicted 31.0 deaths and demonstrated good calibration (standardized incidence ratio [SIR]: 0.97; 95% CI: 0.68, 1.38) and discrimination (c-statistic: 0.71). The ILD-GAP score reduced the predicted mortality risk, so only 18.3 deaths were predicted within 3 years of ILD diagnosis, this demonstrated poor calibration (SIR 1.64; 95%CI 1.15, 2.35).

Conclusion:  In this large single-center cohort of patients with RA-ILD, most patients were seropositive and had a history of smoking. RA-ILD is associated with decreased survival, similar for NSIP and UIP. The GAP model may be useful in informing prognosis and patient management.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/patterns-of-interstitial-lung-disease-and-associated-mortality-in-rheumatoid-arthritis/