Longitudinal associations between body mass index and disease activity, and radiographic progression in rheumatoid arthritis patients receiving infliximab

Background: Current literature suggests that overweight and obese patients with rheumatoid arthritis (RA) have increased disease activity scores but decreased radiographic joint damage (given mainly cross sectional analysis with categorical variables).

Objectives: This study aimed to assess the longitudinal associations between body mass index (BMI) and RA disease activity, and radiographic progression, during infliximab treatment courses (a tumour necrosis alpha inhibitor [TNFi] dosed according to weight).

Methods: We included all infliximab users with an RA diagnosis in the Swiss Clinical Quality Management of Rheumatic Diseases (SCQM) registry [1997-2020]. Two cohorts were identified: 1) starting from a first BMI or RA disease activity (DAS28-esr score) record (cohort 1), and 2) from a first BMI or radiographic progression (Rau score) record (cohort 2). We evaluated the coefficient and 95% confidence interval (CI) of BMI with changes in mean DAS28 esr changes (cohort 1) and mean Rau scores (cohort 2) using generalized estimation equations (GEE), overall, and stratified by BMI categories. We specified various models adjusting for confounders (e.g. age, sex) and potential mediators (e.g. co-medication, comorbidities) to assess their influence.

Results: Cohort 1 comprised 412 patients (74% women, mean age 53 years, mean BMI 25 kg/m2). Overall, there was no change in mean DAS28-esr given increasing BMI (adj. BMI coeff.: 0.00, 95% CI 0.02 – 0.02). We observed a most extreme result in underweight patients (n=28), where an increase of 1 in BMI resulted in a non-significant decrease of 0.14 in mean DAS28 esr (adj. BMI coeff.: -0.14, 95% CI -0.28 – 0.01). Cohort 2 comprised 187 patients very similar to those in cohort 1. There was a statistically significant decrease of 1.05 in mean Rau scores for every increase of 1 in BMI (adj. BMI coeff.: -1.05, 95% CI -1.92 – -0.19). Results were statistically non-significant across BMI categories. For both cohorts, varying adjusting variables did not change the results largely.

Conclusions: Our longitudinal investigation suggests that, overall, BMI increase does not lead to a change in DAS28-esr in patients treated with weight dosed TNFi. Yet, a slight non significant decrease in DAS28-esr with increasing BMI in underweight patients may yield insights into this difficult and under-researched RA phenotype. Furthermore, a decrease in radiographic joint damage with increasing BMI in the overall population suggests a protective effect not limited to overweight / obese populations. No mediating effects were observed for co-medication or comorbidities.