SAT0073 MYOPENIA AGGRAVATES RHEUMATOID ARTHRITIS IN ELDERLY PATIENTS AS A MEDIATOR
Authors: J. D. MA, C. Chen, J. Z. Lin, Q. H. LI, L. F. Chen, Y. H. Xu, D. H. Zheng, L. Dai
Journal: Annals of the Rheumatic Diseases (2020)

Background: Ageing affects different systems resulting in a special clinical phenotype of rheumatoid arthritis (RA) in elderly patients who are characterized by higher level of systemic inflammatory and poor function. It also leads to loss of muscle mass causing functional limitation and reduced quality of life. However, little is known about muscle loss in growing elderly RA patients. Objectives: To explore the characteristics of muscle mass and clinical significance in elderly RA patients. Methods: Consecutive RA patients were recruited and clinical data including disease activity (DAS28-CRP), function (HAQ-DI) and radiographic indicators (modified Sharp score) were collected. The mass and distribution of muscle were assessed by bioelectric impedance analysis. Myopenia was defined as appendicular skeletal muscle mass index (ASMI) ≤7.0kg/m 2 in men and ≤5.7kg/m 2 in women. Results: (1) There were 643 RA patients recruited with 82.3% female, mean age 49.7±12.9 years and median disease duration 48 (IQR 21,108) months. There were 414 (64.4%) RA patients with active disease (DAS28-CRP≥3.2) and 229 (35.6%) with remission. (2) There were 165 (25.7%) elderly RA patients (age≥60 years) with mean age 65.1±4.5 years. Compared with young patients (age&lt;60 years), elderly RA patients had significantly higher disease activity indicators including PtGA, PrGA, ESR, CRP, DAS28-CRP, DAS28-ESR, SDAI and CDAI, higher HAQ-DI (0.38 vs. 0.13) and higher modified total Sharp score (mTSS, 16 vs. 9, all P &lt;0.001). There were 288 (44.8%) RA patients with myopenia and elderly RA patients had higher proportion of myopenia than young patients (54.5% vs. 41.4%, P =0.003). (3) Among 4 subgroups according to age and ASMI, elderly RA patients with myopenia ( n =90, 14.0%) had significant higher DAS28-CRP (3.6 vs. 3.0), higher HAQ-DI (0.50 vs. 0.12) and higher mTSS (21 vs. 7) than those in young patients without myopenia ( n =280, 43.5%), and had higher mTSS (21 vs. 10) than those in elderly patients without myopenia ( n =75, 11.7%, all P &lt;0.0083). (4) Adjusted for confounding factors including gender, disease duration, BMI, smoking habit, RF, ACPA and treatment naïve, multiple linear regression analysis showed that age was positively correlated with DAS28-CRP ( β =0.010), HAQ-DI ( β =0.003) and mTSS ( β =0.005, all P &lt;0.05), while ASMI was negatively correlated with DAS28-CRP ( β = -0.445), HAQ-DI ( β = -0.124) and mTSS ( β = -0.247, all P &lt;0.001). (5) Mediation analysis showed that old age (≥60 years) had total effect on DAS28-CRP ( β =0.353), HAQ-DI ( β =0.132) or mTSS ( β =7.909, all P &lt;0.05), but no direct effect on them (all P&gt; 0.05). ASMI fully mediated the associations between old age and DAS28-CRP, HAQ-DI or mTSS. Conclusion: Half of elderly RA patients manifest myopenia which aggravates the whole disease of disease activity, joint function and destruction as a mediator. Myopenia, a neglected comorbidity in elderly RA should be emphasized. Funding: This work was supported by National Natural Science Foundation of China (81801606 and 81971527,), Natural Science Foundation of Guangdong Province (2018A030313541 and 2019A1515011928), Science and Technology Program of Guangzhou (201904010088). Disclosure of Interests : None declared