Introduction Greater body mass index (BMI) has been associated with less radiographic progression in rheumatoid arthritis (RA). We evaluated the association between BMI and joint damage progression as measured by X-ray and MRI.

Methods 1068 subjects with RA from two clinical trials of golimumab (GO-BEFORE and GO-FORWARD) had radiographs performed at weeks 0, 52 and 104 and evaluated using the van der Heijde–Sharp (vdHS) scoring system. Contrast-enhanced MRIs of the dominant wrist and hand were obtained at weeks 0, 12, 24, 52 and 104. Multivariable logistic regression evaluated the risk of radiographic progression for each BMI category (<25, 25–30, >30 kg/m²). Within GO-BEFORE, piecewise, robust generalised estimating equations marginal models assessed the probability of MRI erosion progression for each BMI category. Multivariable linear regression models assessed baseline associations between BMI and bone oedema (a precursor of bone erosion).

Results Higher BMI category was associated with a lower probability of progression in vdHS score at weeks 52 and 104 independent of potential confounders. Higher BMI was also independently associated with a lower probability of progression in MRI erosion score over 2 years. Subjects with greater BMI demonstrated less bone oedema independent of differences in other disease severity measures, including MRI synovitis in the same joints.

Conclusions Greater BMI is associated with a lower risk of progression on X-ray and MRI over 2 years. Subjects with greater BMI also demonstrate less bone oedema at baseline. Greater BMI may indicate a less aggressive RA phenotype and aid in risk stratification.