The equivocal opposite effects of lower and higher body mass index at diagnosis on radiographic joint damage progression in early rheumatoid arthritis: an inception cohort study over 15 years

Objective To investigate the effect of Body Mass Index (BMI) on long-term radiographic damage in an inception rheumatoid arthritis (RA) cohort. Methods The study population, n=1813, originated from the observational Better AntiRheumatic FarmacoTherapy cohort. X-rays of hands and feet at inclusion, 1, 2, 5, 8 and 15 years were quantified for erosion score (ES), joint space narrowing (JSN) and the sum of modified Sharp-van der Heijde total score (mTSS). Patients were grouped by baseline BMI categories, including additional cut-off BMI ≥27 kg/m 2 . Curve estimation regression analysis and multivariate mixed models were performed. Results Inverse relationship between BMI and log-transformed mTSS was identified. In general, patients with higher BMI, compared with normal weight and/or underweight patients, had more favourable radiographic outcomes defined by annualised progression rates of mTSS, ES and JSN, less frequent rapid and clinically relevant radiographic progression, and maintained structural integrity. In contrast to consistently higher 28-joint Disease Activity Score (DAS28) levels, BMI ≥30 kg/m 2 was associated with less severe mTSS progression, beta=0.946 (95% CI 0.902 to 0.995) per year, p=0.029, while BMI ≤20 kg/m 2 with more joint damage, beta=1.091 (1.019–1.169) per year, p=0.014. The findings were confirmed in separate analyses regarding ES and JSN, and in anticitrullinated protein antibody-positive patients. The effect sizes of association between mTSS change and over time levels of C-reactive protein, erythrocyte sedimentation rate and DAS28 declined over time and varied across BMI strata. The latter finding indicates effect modification by BMI. The results in BMI ≥27 kg/m 2 group largely mirrored those in BMI ≥30 kg/m 2 . Conclusions BMI is one of the determinants of radiographic progression in early RA. Lower and higher BMI have opposite effects on radiographic progression.