Phase Angle as a Marker of Physical Function in Non-Sarcopenic Rheumatoid Arthritis

Background: Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease. Most patients with RA face a barrier to participation in social activities or exercise due to joint pain, despite the beneficial effects of exercise and physical activity. Thus, RA may be a risk factor for sarcopenia in the clinical field. Bioelectrical impedance analysis-derived phase angle (PhA) reflects cellular health and is correlated with the prognosis of various diseases. However, its association with physical function in non-sarcopenic RA female patients remains unclear. We evaluated the association between PhA values and various physical function measures in female patients with non-sarcopenic RA. Methods: Thirty-five participants with RA were screened. One met the criteria for sarcopenia. Finally, 34 patients with non-sarcopenic RA were enrolled. This cross-sectional retrospective study evaluated upper- and lower-extremity strengths, cross-sectional area of rectus femoris, 6 min walking test, Borg scale score, sit-to-stand test, and physical function and mental health from 36-Item Short Form Health Survey scores. Results: In total, 34 female participants (mean age = 49.74 ± 8.15 years) were enrolled. In non-sarcopenic RA patients, PhA was significantly correlated with BMI and ASM/(height)². Multicollinearity was not detected among the independent variables (VIF < 5). The final multivariable regression model identified ASM/height² as a significant predictor of PhA among non-sarcopenic RA patients. Conclusion: Multivariable linear regression analyses identified appendicular skeletal muscle mass as a significant predictor of PhA. Bioelectrical impedance analysis-derived PhA is a valuable guidance tool for RA management. PhA can be a useful clinical biomarker of muscle status in non-sarcopenic RA patients.