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

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ObjectivesTo describe comorbid conditions in patients with rheumatoid arthritis–associated interstitial lung disease (RA-ILD) and to analyze factors associated with multimorbidity. MethodsNested 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 conditions 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. ResultsThe 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). ConclusionIn patients with RA, multimorbidity was associated with ILD, systemic inflammation, and advanced age.