A direct association has been found between increased BMI and increased swelling of LE joints in RA patients, as evident from a study published in Journal of Clinical Rheumatology. As the evaluation of disease activity in obese rheumatoid arthritis (RA) patients is challenging, a study was recently carried out to examine the measures set by the American College of Rheumatology (ACR) used in assessing RA disease activity with the specific focus on the swollen joint count (SJC).

Ranganath VK, et al. evaluated the cross-sectional cohort of 323 early seropositive RA patients (symptom duration ≤15 months). Biologic-naive patients had  ≥ 6/44 SJC and ≥ 9/44 tender joint count. All the ACR core measures viz. the Disease Activity Score (DAS) 44/erythrocyte sedimentation rate (ESR), DAS28/ESR4 item, Clinical Disease Activity Index (CDAI), and body mass index (BMI) were collected and compared between BMI categories. The relationship between high BMI (≥30 kg/m) and lower-extremity (LE) SJC and SJC44 while accounting for other ACR measures were assessed by multivariable linear regression models.

It was found that the Disease Activity Score 44/ESR4 item, Health Assessment Questionnaire Disability Index, physician global, and SJC44 differed across BMI categories (P < 0.05). It was also observed that the metacarpophalangeal joints and LE joints (knees, ankles, metatarsophalangeal joints) of patients with SJC44 were associated with increased swelling in all BMI groups (P < 0.05).

The study findings determined an increase in DAS44– measured disease activity in obese RA patients due to increased LE swollen joints. However, Clinical Disease Activity Index and Disease Activity Score 28 which assessed upper-extremity joint, are not significantly influenced by obesity.