Background/Purpose:  Studies report that obese and overweight patients with rheumatoid arthritis (RA) are less likely to attain remission and more likely to have limited therapeutic response, as compared to non-obese RA patients. Our objective was to determine the association between synovitis musculoskeletal ultrasound measures (Power Doppler [PDUS]) and disease activity measures (DAS28) in obese RA patients.

Methods:  Cross sectional clinical and ultrasound data was collected on 43 RA patients, and divided into three groups based on their body mass index (BMI): <25, 25 to 30, and >30. Clinical joint assessments included patient global visual analogue scale (VAS), physician global VAS and 28 swollen and tender joint counts. The sedimentation rate, anti-cyclic citrullinated pepide (ACPA) and rheumatoid factor (RF) were also measured. DAS28/ESR-4 item and clinical disease activity index (CDAI) were calculated. Ultrasound of the wrist, metacarpalphalangeal joints 2, 3 and 4, proximal interphalgeal joints 2 and 3 and metatarsalphalangeal joints 2 and 5 included synovitis assessments with gray scale (GSUS) and PDUS of the most affected side.  GSUS and PDUS were categorically scored as per OMERACT published guidelines on a scale of 0-3. We then categorized the 0-3 scale into two PDUS groups 0/1=non-active, 2/3=active synovitis. Demographic and clinical characteristics were compared across BMI groups with Kruskal-Wallis test (KW) for continuous variables and chi-square tests for categorical variables. Mixed effects models were used to evaluate the relationship between BMI and the PPV and NPV.

Results:  Demographic characteristics and disease activity were similar among BMI groups; however, PDUS scores significantly differed as seen in the Table. Using PDUS activity as the gold standard for synovitis and clinically swollen joints (SJ) as the test, the positive predictive value (PPV) of SJ was lower in higher BMI groups and significantly different across the BMI groups in KW analysis (0.71 in BMI<25, 0.58 in BMI 25-30 and 0.44 in BMI<30) (p= 0.01). Similarly, the negative predicative value (NPV) was significantly higher in higher BMI groups (p=0.04). In the mixed effects models, BMI was significantly predictive of PPV and a one unit increase in BMI was associated with a 0.1 unit decrease in PPV (p=0.02). BMI was not significantly predictive of NPV in the mixed effects model.

Conclusion: This study suggests that for obese RA subjects, clinically swollen joints have a higher PPV and a trend for lower NPV for true synovitis, while the opposite is found for normal BMI patients. This implies that clinically assessed swollen joints are less likely to represent true synovitis in obese RA patients. Therefore, RA disease activity may be overestimated by CDAI and DAS28 calculations in this subpopulation.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/less-musculoskeletal-ultrasound-power-doppler-activity-seen-in-obese-rheumatoid-arthritis/