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Associated comorbidities can bias clinical disease activity measures.
Patients who had rheumatoid arthritis and were obese were less likely to achieve remission based on the Disease Activity Score using 28 joints and C-reactive protein (DAS28-CRP), compared with those who were not obese, in a recent study.
When disease activity was assessed with MRI of joints, rates of low disease activity were similar in patients with rheumatoid arthritis who were obese and those who had a normal body mass index (BMI).
Obesity is not associated with more severe rheumatoid arthritis.
Obesity has been linked to refractory rheumatoid arthritis in earlier research because it is one of the most prominent comorbidities, but Michael George and colleagues at the University of Pennsylvania School of Medicine and other centers proposed that obesity may instead create bias in calculating disease activity scores, leading to a false perception of cause and effect.
MRI is a sensitive and noninvasive way to assess synovitis and bone edema as well as predict the progression of joint damage independent of clinical disease activity scoring, the authors noted.
They sought to define the impact of obesity on clinical and radiographic disease activity in rheumatoid arthritis and presented their findings in a recent Annals of the Rheumatic Diseases article.
Included were 470 patients from the GO-BEFORE (Golimumab Before Employing Methotrexate as the First-Line Option in the Treatment of Rheumatoid Arthritis of Early Onset) trial, a randomized, multicenter, double blind, placebo controlled study. Patients who had rheumatoid arthritis with a BMI less than 25 (N=214), were compared with those who had a BMI greater than 30 (N=255). DAS28-CRP scores were compared with MRI evidence of joint damage.
• Patients with rheumatoid arthritis who were overweight or obese had higher tender joint counts and worse Health Assessment Questionnaire (HAQ) scores at baseline than normal weight subjects.
• DAS28-CRP scores were similar between the groups.
• The occurrence of bone edema and fewer erosions at baseline was much lower in overweight and obese patients with rheumatoid arthritis than in normal weight counterparts.
• Looking at DAS28-CRP at 24 weeks, remission rates were 28%, 28%, 27%, and 17% for patients with rheumatoid arthritis who were underweight, normal weight, overweight, and obese, respectively.
• After adjustment, obese patients with rheumatoid arthritis were less likely to achieve remission based on disease activity scores or a low HAQ score than normal weight patients (odds ratio [OR], 0.47; 95% confidence interval [CI], 0.24 to 0.92; p=0.03, and OR, 0.49; 95% CI, 0.28 to 0.89; p=0.02, respectively).
• Obese patients with rheumatoid arthritis were more likely to have less favorable patient global scores ≤ 1 (OR, 0.47; 95% CI, 0.24 to 0.92; p=0.03) and less likely to have a CRP level of ≤ 1mg/dL (OR, 0.44; 95% CI, 0.23 to 0.84; p=0.01) at 24 weeks.
• Based on MRI, rates of low synovitis were the same between groups.
• Low bone edema scores were more common among obese patients versus normal weight patients (69% vs. 50%; OR, 2.06; 95% CI, 1.10 to 3.84; p=0.02). However, after adjustment there was no difference in bone edema between groups (OR, 1.01; 95% CI, 0.40 to 2.51; p=0.99).
• At 52 weeks, obese patients with rheumatoid arthritis had higher tender joint counts when compared with normal weight patients (OR, 0.47; 95% CI, 0.27 to 0.82; p=0.01).
Implications for physicians
• Physicians should not let obesity as a rheumatoid arthritis comorbidity cloud their assessments of disease activity.
• Clinical measures of disease activity in rheumatoid arthritis could be biased by obesity.
• Obese patients realize less bone edema and similar joint inflammation than those with normal weight despite regularly having worse disease activity scores.
• Care should be taken in assessing the impact of any comorbidity in rheumatoid arthritis. Objective measures such as MRI can be helpful in diagnosis and prognosis.
Support was provided for the study by the Rheumatology Research Foundation Scientist Development Award and a Veterans Affairs Clinical Science Research & Development Career Development Award.
George MD, Mikkel Ostergaard M, Conaghan PG, et al. “Obesity and rates of clinical remission and low MRI inflammation in rheumatoid arthritis.” Ann Rheum Dis. 2017 Oct;76(10):1743-1746. doi: 10.1136/annrheumdis-2017-211569. Epub 2017 Jun 12.