Muscle wasting, a neglected complication associated with physical dysfunction in elderly patients with rheumatoid arthritis: a cross-sectional observational study

Objective: Little is known about muscle wasting in elderly patients with rheumatoid arthritis (RA). We examined muscle characteristics and their clinical significance in this group. Method: Consecutive RA patients were recruited and clinical data were collected. Muscle mass and distribution were assessed using bioelectric impedance analysis. Myopenia was defined as an appendicular skeletal muscle mass index (ASMI) <= 7.0 kg/m(2) (men) and <= 5.7 kg/m(2) (women). Results: Among the 643 RA patients recruited, 165 (25.7%) were elderly patients (age >= 60 years) with a mean age of 65.1 +/- 4.5 years. Compared with young patients (age < 60 years), elderly RA patients had significantly higher Disease Activity Score based on 28-joint count-C-reactive protein (DAS28-CRP) (median 3.4 vs 3.2), Health Assessment Questionnaire Disability Index (HAQ-DI) (0.38 vs 0.13), and modified total Sharp score (mTSS) (16 vs 9), and a higher proportion of myopenia (54.5% vs 41.4%; all p < 0.01). Elderly RA patients with myopenia (n = 90, 14.0%) had significantly higher DAS28-CRP (3.6 vs 3.0), HAQ-DI (0.50 vs 0.12), and mTSS (21 vs 7) than young RA patients without myopenia (n = 280, 43.5%; all p < 0.0083). Multivariate logistic and linear regression analyses showed that myopenia, high HAQ-DI, active smoking, hypertension, diabetes, and coronary atherosclerotic heart disease were the main relevant characteristics of elderly RA patients. Age positively correlated with HAQ-DI, and ASMI negatively correlated with HAQ-DI (both p < 0.01). Further mediation analysis showed that ASMI partially mediated the association between age and HAQ-DI. Conclusion: Our data reveal that half of elderly RA patients manifest myopenia which aggravates physical dysfunction as a mediator of age. Myopenia, a neglected complication in elderly RA patients, should be recognized and further investigated.