Body mass index and the rheumatoid arthritis swollen joint count: an observational study

Obesity is a prevalent condition and a serious health concern. The relationship between obesity and rheumatoid arthritis (RA) disease activity and severity has not been adequately examined, and there are concerns that periarticular adipose tissue may reduce the utility of the joint examination.

We used a cross-sectional study to compare the performance of swollen joint count (SJC) in subjects with RA across body mass index (BMI) strata. Specifically, regression techniques tested for associations of SJC and 7 RA disease activity/severity measures (including high-sensitivity C-reactive protein level, radiographic changes, and Multidimensional Health Assessment Questionnaire scores) within BMI quartiles. We also evaluated the association of BMI with radiographic evidence of RA in multivariate analyses and the association of BMI with SJC. Clinical and laboratory data from 980 Veterans Affairs Rheumatoid Arthritis registry participants were analyzed using linear and logistic regression.

Associations were evident between SJC and 6 of the 7 examined RA disease activity/severity measures. SJC predicts RA disease activity/severity in more obese subjects at least as well as in subjects with lower BMIs, and there was a trend toward better performance in individuals with higher BMIs. Subjects with higher BMIs were marginally less likely to be characterized by radiographic changes (odds ratio 0.98, P = 0.051). We found no association between BMI and SJC.

BMI does not obscure the relationship of SJC and objective disease activity measures. There is a borderline association of higher BMI and the likelihood of radiographic changes characteristic of RA after controlling for clinical characteristics.