Association between chronic obstructive pulmonary disease, smoking, and interstitial lung disease onset in rheumatoid arthritis.

OBJECTIVES

In rheumatoid arthritis (RA), respiratory manifestations include chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD). We assessed whether baseline COPD and smoking were associated with RA-ILD onset.

METHODS

We identified new-onset ILD in incident RA subjects within the MarketScan Commercial Claims database, using physician and/or hospitalisation diagnostic codes. Smoking data (current, past, never) were available for a subset via a health questionnaire. Kaplan-Meier analyses assessed time to ILD onset, stratified by prior COPD and smoking. Multivariate Cox regression models were adjusted for age, sex, and (in the subset) smoking. Sensitivity analyses adjusted for past RA drugs.

RESULTS

Among 373,940 new RA subjects, 6343 (1.7%) developed ILD (8.1 events per 1000 person-year, 95% CI 7.9, 8.3). ILD was more common among subjects with baseline COPD. Adjusting for age and sex, the hazard ratio (HR) between baseline COPD and incident ILD was 2.15, 95% CI 1.93, 2.39. We could not establish a clear relationship between current smoking and ILD; in the subset with smoking data, the HR point estimate for COPD was similar but the 95% CI was wider (due to fewer subjects) and included the null value. Adjusting for baseline RA drugs did not change results.

CONCLUSIONS

Pre-existing COPD in incident RA subjects was associated with higher risk of future ILD. While a trend persisted after adjusting for smoking, we were limited by reduced sample size. Our study highlights the importance of ongoing assessments of potentially complicated relationships between smoking, COPD, and other factors in RA-associated ILD.