Rheumatoid arthritis lung disease. Determinants of radiographic and physiologic abnormalities

Objective. To determine the prevalence and important clinical predictors of radiographic and physiologic abnormalities indicative of rheumatoid arthritis interstitial lung disease (RA-ILD). Methods. An unselected cohort of patients with a confirmed diagnosis of RA and known lung disease were identified (n = 336) and evaluated for RA disease activity and severity. Outcomes included abnormalities determined by the pulmonary function tests of forced vital capacity (FVC) and diffusion capacity for carbon monoxide (DLco), and/or chest radiographic findings of interstitial infiltrates. We used multivariable statistical modeling to determine the independent significance of cigarette smoking and other RA-specific factors on the pulmonary abnormalities of interest. Results. At least 1 of the 3 abnormal findings was identified by pulmonary tests in 32.4% of all patients. These abnormal findings included an FVC <80% of predicted in 42 patients, a DLco <80% of predicted in 64 patients, and evidence of radiographic interstitial infiltrates in 40 patients. After statistical adjustment for confounding factors, pack-years of cigarette smoking remained a significant predictor of low DLco (β = −0.07, 95% confidence interval [95% CI] −0.09, −0.04), low FVC (β = −0.003, 95% CI −0.006, −0.0004), and interstitial abnormalities on chest radiograph (odds ratio for ⩾25 pack-years = 3.76, 95% CI 1.59, 8.88). The Health Assessment Questionnaire (HAQ) Disability Index (DI) was also an important risk factor for the decline in both the DLco (β = −1.15, 95% CI −2.00, −0.30) and FVC (β = −0.23, 95% CI −0.32, −0.13). Conclusion. Although RA disease activity/severity (particularly as defined by the HAQ DI) was important, smoking was the most consistent independent predictor of radiographic and physiologic abnormalities suggestive of ILD in RA.