Localized low muscle mass is associated with hand dysfunction beyond inflammation in rheumatoid arthritis: a...

While systemic muscle loss is associated with physical dysfunction, the role of localized upper extremities muscle deterioration in hand disability remains unclear in rheumatoid arthritis (RA). We aimed to explore the impact of low muscle mass in upper extremities on hand dysfunction in patients with RA.

This cross-sectional study was conducted in a Chinese RA population and control subjects. Demographic and clinical data were collected. Hand function assessment included handgrip strength and hand disability according to the Stanford Health Assessment Questionnaire-Disability Index (HAQ-DI). Muscle mass was assessed using bioelectrical impedance analysis and muscle mass index of upper extremities (MMI_UE) was calculated. Logistic regression analyses evaluated associations between MMI_UE and hand dysfunction.

A total of 1,104 RA patients and 3,281 control subjects were included in this study. RA patients exhibited lower MMI_UE compared with controls (1.42 ± 0.32 vs. 1.73 ± 0.40 kg/m², P < 0.001). The prevalence of low MMI_UE was higher in RA patients (45.9%, 507/1104) than in controls (14.5%, 475/3,281, P < 0.001). Among RA patients, 57.2% (632/1,104) had low handgrip strength and 39.6% (437/1,104) had HAQ-DI hand disability. RA patients with low MMI_UE showed significantly poorer hand function than those with normal MMI_UE, including lower handgrip strength (14.59 ± 6.78 vs. 18.67 ± 8.14 kg), higher prevalence of low handgrip strength (70.0% vs. 46.4%) and HAQ-DI hand disability (46.9% vs. 33.3%, all P < 0.001) than those with normal MMI_UE. Logistic regression analyses showed that RA patients with low MMI_UE had higher risks of low handgrip strength (AOR = 2.44, 95% CI [1.84-3.23], P < 0.001) and HAQ-DI hand disability (AOR = 1.59, 95% CI [1.15-2.19], P = 0.005).

The present cross-sectional study demonstrates that localized low muscle mass of the upper extremities is associated with hand dysfunction in RA, independent of inflammation. These findings support the need for further longitudinal studies to explore the potential benefits of incorporating routine muscle assessments into RA care.