Analysis of comorbidity in rheumatoid arthritis-associated interstitial lung disease: a nested case-cohort study

Objectives: To describe comorbid conditions in patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD) and to analyze factors associated with multimorbidity. Methods: Nested case-cohort study of 2 prospective cohorts: one with RA-ILD (cases) and another with RA but not ILD (controls). The cohorts were matched for age, sex, and time since diagnosis. Multimorbidity was defined as the co-occurrence of 2 or more chronic diseases, in addition to RA and ILD. We evaluated the comorbid con-ditions included in the Charlson Comorbidity Index, cardiovascular risk factors, neuropsychiatric conditions, and other frequent conditions in RA. We also recorded clinical-laboratory variables, inflammatory activity according to the 28-joint Disease Activity Score, C-reactive protein (CRP), physical function, and pulmonary function. We performed 2 multivariate analyses to identify factors associated with multimorbidity in RA and RA-ILD. Results: The final study population comprised 110 cases and 104 controls. Multimorbidity was more frequent among cases than controls (80 [72.7] vs 60 [57.7]; p = 0.021). In both groups, multimorbidity was associated with ILD (OR [95% CI] 1.92 [1.03-3.59]; p = 0.039), age (OR [95% CI] 1.05 [1.01-1.08]; p = 0.004), CRP (OR [95% CI] 1.16 [1.05-1.29]; p = 0.003), and erosions (OR [95% CI] 1.05 [1.01-1.08]; p = 0.004); in the cases, it was associated with CRP (OR [95% CI] 1.17 [1.01-1.35]; p = 0.027), anti-citrullinated peptide antibody (OR [95% CI] 1.23 [1.14-13.02]; p = 0.049), and forced vital capacity (OR [95% CI] 0.79 [0.96-0.99]; p = 0.036).