Muscle morphology changes over 1-year in patients with rheumatoid arthritis: a prospective cohort study using muscle ultrasound.

BACKGROUND

Low muscle mass is associated with physical disability in rheumatoid arthritis (RA), highlighting the need for regular muscle assessment. Muscle ultrasound (MU) is a promising tool for evaluating muscle morphology, however, longitudinal studies in RA are lacking. This study aimed to evaluate changes in quadriceps muscle thickness and pennation angle using MU and identify predictors of these changes.

METHODS

This prospective observational cohort included women and men with RA. Muscle thickness and pennation angles of the rectus femoris (RF), vastus intermedius (VI), and vastus lateralis (VL) were assessed using MU. Disease activity was measured using the 28-joint Disease Activity Score based on C-reactive protein (DAS28-CRP), muscle strength by the handgrip test, physical performance by Short Physical Performance Battery (SPPB), physical disability by Health Assessment Questionnaire (HAQ), and physical activity by International Physical Activity Questionnaire (IPAQ). Paired t-tests, Pearson and Spearman correlations analyses, and multiple linear regression were conducted (p≤0.05).

RESULT: Among 155 RA patients (88.4% women), 106 completed the 1-year follow-up. The baseline mean age was 58.7±9.5 years, median disease duration was 11.0 (6.0-20.0) years, and mean DAS28-CRP was 3.02±1.29. At follow-up, women exhibited a 7% reduction in VL, 6% in RF, and 4% in VI pennation angles (p≤0.05). Men showed a 39% increase in RF and a 29% in VI muscle thickness (p≤0.05). In women, lower baseline DAS28-CRP and higher muscle strength were correlated with increased muscle thickness (p≤0.05), with DAS28-CRP identified as a predictor of changes in muscle thickness (β=-0.058; CI95%,-0.114 to -0.003).

CONCLUSION

RA women exhibited a decrease in pennation angle, while men had an increase in muscle thickness over time. Disease activity was a significant predictor of these changes in women, underscoring MU's clinical utility.