Body mass index (BMI) might affect rheumatoid arthritis (RA) outcomes. Clinical assessment of swollen joint count (SJC) might also be affected by obesity in terms of obesity-related excess adipose tissue. In this study, we compared ultrasonography (US) and clinical examination in assessing the effect of BMI on RA disease activity assessment.
This was a single-centre study including RA (ACR/EULAR criteria) patients. US assessment was performed by one trained rheumatologist blinded to clinical data. US synovitis was defined as grey-scale score ≥2 and/or power Doppler score ≥1. The primary outcome measure was difference in SJC (ΔSJC) between clinical and US assessment (US-clinical examination). The secondary outcome was to evaluate the difference between clinical and US assessment of the Disease Activity Score in 28 joints (ΔDAS28) in the 3 BMI subgroups according to the WHO classification.
We included 76 RA patients (mean age 53.8 ± 11.8 years; 67% female). Overall, 28 (36.8%), 33 (43.4%) and 15 (19.7%) were normal weight, overweight and obese, respectively. Baseline characteristics did not differ between the 3 BMI subgroups. US-determined SJC was significantly higher than clinical-determined SJC for overweight and obese RA patients: p=0.001 and p=0.049, respectively. The DAS28 was higher with US than clinical examination within the overweight group only (p=0.002). One-way analysis of variance (ANOVA) revealed a significant difference between ΔDAS28 among the 3 BMI subgroups (p=0.046).
In high BMI RA patients both SJC and DAS28 seem to be undervalued by clinical assessment when compared to US.