To determine the prevalence and important clinical predictors of radiographic and physiologic abnormalities indicative of rheumatoid arthritis interstitial lung disease (RA-ILD).
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.
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 (beta = -0.07, 95% confidence interval [95% CI] -0.09, -0.04), low FVC (beta = -0.003, 95% CI -0.006, -0.0004), and interstitial abnormalities on chest radiograph (odds ratio for > or = 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 (beta = -1.15, 95% CI -2.00, -0.30) and FVC (beta = -0.23, 95% CI -0.32, -0.13).
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.