For patients with rheumatoid arthritis (RA), myopenia is very common and is associated with functional limitation and joint damage, according to results published in the Journal of Cachexia, Sarcopenia and Muscle.
The study included participants with RA (n=457) and healthy controls (n=1860). The researchers assessed participants’ body composition, using bioelectric impedance analysis. Overfat was defined as body fat percentage (BF%) ≥25% for men and ≥35% for women. Myopenia was defined as appendicular skeletal muscle mass index ≤7.0 kg/m2 in men and ≤5.7 kg/m2 in women.
The researchers collected data on body mass index, disease activity, function, and radiographic assessment. They defined active disease as disease activity score in 28 joints with 4 variables including C-reactive protein (DAS28-CRP) ≥2.6. Functional limitation was defined as a Stanford Health Assessment Questionnaire Disability Index >1. Radiographic joint damage (RJD) was defined as Shaper/van der Heijde modified sharp score >10.
After comparing body mass index and body composition among participants with RA and control patients, the researchers found that participants with RA had lower body mass index (17.7% underweight) and lower appendicular skeletal muscle mass index (45.1% myopenia) compared with control patients.
Compared with those without myopenia, participants with RA and myopenia had significantly higher DAS28-CRP (median, 3.5 vs 3.0), higher Stanford Health Assessment Questionnaire Disability Index (median, 0.38 vs 0.13) with a higher rate of functional limitation (24.8% vs 7.6%), higher modified sharp score (median, 22.3 vs 9.0), and more RJD (71.8% vs 45.8%; all P<.001).
After performing multivariate logistic regression analysis, the researchers found that myopenia was positively associated with functional limitation (odds ratio, 2.546; 95% CI, 1.043-6.217) and RJD (odds ratio, 2.660; 95% CI, 1.443-4.904).
After adjusting for confounding factors, the results indicated that overfat and myopenia had significant additive interactions with active disease (attributable proportion due to additive interaction, 0.528; 95% CI, 0.086-0.971), functional limitation (attributable proportion due to additive interaction, 0.647; 95% CI, 0.356-0.937), and RJD (attributable proportion due to additive interaction, 0.514; 95% CI, 0.139-0.890).
“Further research on the underlying mechanism and the effect of skeletal muscle mass improvement in RA management are worth exploring in [a] large study,” the researchers wrote.
Li J, Liang J, Ma J, et al. Myopenia is associated with joint damage in rheumatoid arthritis: a cross-sectional study [published online January 30, 2019]. J Cachexia Sarcopenia Muscle. doi: 10.1002/jcsm.12381