BASELINE PREVALENCE AND FACTORS ASSOCIATED WITH INTERSTITIAL LUNG DISEASE IN TWO RHEUMATOID ARTHRITIS INCEPTION COHORTS IN THE UK

Background Rheumatoid arthritis (RA) is a chronic, inflammatory disease with interstitial lung disease (ILD) being an important extra-articular manifestation, associated with significant morbidity and mortality. Objectives To determine the prevalence of ILD at time of RA diagnosis and identify baseline independent factors associated with ILD. Methods Two early inception cohorts (1986-2001) were used: the early RA network (ERAN) and the early RA study (ERAS). Socio-demographic, clinical and laboratory measures were recorded at baseline, 6 months and yearly thereafter. Baseline variables collected and included in analyses were: seropositivity, body mass index (BMI), ethnicity, measures of deprivation, smoking status. Comorbidity burden was evaluated using the rheumatic disease comorbidity index (RDCI). Baseline prevalence (proportion of individuals with ILD at baseline) and 95% confidence interval was estimated. Multivariable regression analyses were performed to identify risk factors at baseline associated with RA-ILD development. Multiple imputation was used for missing data. Results Data from a total of 2701 patients were included in the study, from whom 101 patients were diagnosed with ILD. Follow up was up to 25 years (mean 6.8 years); 75% of patients followed for ≥10 years. Of these, 12% had ILD at baseline; 46% were diagnosed with ILD during follow up and 43% were diagnosed with ILD post-mortem. The estimated prevalence of ILD at baseline was 0.44% (95% CI 0.19% to 0.69%). Univariable analyses of baseline factors showed age at onset (p