A NEW study investigated whether body mass index (BMI) influences the incidence or progression of distal interphalangeal (DIP) joint osteoarthritis (OA) in patients with rheumatoid arthritis (RA), revealing that BMI may not play a significant role in this specific joint pathology. While obesity is a well-established risk factor for OA and RA, its relationship with structural joint damage in RA has remained paradoxical.
BMI Shows No Effect on DIP Joint OA Progression
Researchers analysed data from the Swiss Clinical Quality Management in Rheumatic Diseases registry, including RA patients with a baseline BMI of 18.5 kg/m² or higher. Two patient cohorts were examined: an incidence cohort of 1,031 patients without baseline DIP OA (median follow-up 5.0 years) and a progression cohort of 1,481 patients with baseline DIP OA (median follow-up 4.9 years). DIP joint radiographs were assessed using the modified Kellgren/Lawrence grading system to evaluate OA features, including joint space narrowing (JSN), osteophyte formation, subchondral sclerosis, and central erosions.
Mean baseline BMI was 25.1 kg/m² in the incidence cohort and 26.0 kg/m² in the progression cohort. Over the follow-up period, 24.3% of patients in the incidence cohort developed DIP joint OA, while 67.9% of those in the progression cohort experienced worsening OA. Despite these high rates, multivariable logistic regression analyses found no significant association between BMI and the development or progression of DIP joint OA. Adjusted odds ratios were 1.02 (95% CI 0.98–1.06) for incidence and 1.01 (95% CI 0.98–1.04) for progression. BMI was similarly unrelated to changes in JSN, osteophytes, subchondral sclerosis, or central erosions.
DIP Joint OA May Be Independent of BMI-Related Mechanisms
The findings suggest that, unlike other forms of OA, DIP joint OA in RA may be driven by mechanisms independent of systemic BMI-related factors. This contrasts with the protective effect of higher BMI seen in other RA-related joint damage, highlighting the heterogeneity of joint-specific pathophysiology in RA.
The study underscores the importance of understanding joint-specific disease processes in RA and indicates that strategies targeting systemic risk factors such as BMI may have limited influence on DIP joint OA. Further research is needed to explain the underlying mechanisms that contribute to OA progression in these smaller hand joints.
Reference
Salis Z et al. Association of BMI with radiographic incidence and progression of distal interphalangeal joint osteoarthritis in rheumatoid arthritis patients. Sci Rep. 2025;15:40984.
