Evaluation of Appendicular Muscle Mass in Sarcopenia in Older Adults Using Ultrasonography: A Systematic Review and Meta-Analysis

<b><i>Background:</i></b> The measurement of appendicular muscle mass is essential for the diagnosis of sarcopenia. Ultrasonography is an accurate and convenient method used to evaluate muscle mass. <b><i>Objective:</i></b> The aim of the study was to evaluate the diagnostic value of ultrasonography for appendicular muscle mass in sarcopenia in older adults and find out proper ultrasound parameters. <b><i>Methods:</i></b> Medline, Embase, Cochrane, and Web of Science databases were searched for relevant articles. Published studies on the validity and/or reliability of ultrasonography for quantifying muscle mass of the limbs in sarcopenia in the older population were included. A systematic review was conducted based on specific muscles and reference methods. A meta-analysis was conducted to assess the validity and reliability of the ultrasonography. <b><i>Results:</i></b> Forty articles were included in this review. There were nine, nine, nine, and four studies included in the qualitative synthesis for a diagnostic test, correlation coefficient, intra-class reliability, and inter-class reliability, respectively. The diagnostic value of rectus femoris (RF) or gastrocnemius (GM) thickness on ultrasonography for sarcopenia or low muscle mass was moderate (the area under summary receiver operating characteristic curve [SROC] = 0.76, 95% confidence interval [CI]: 0.72–0.79, SROC = 0.80, 95% CI: 0.76–0.83, respectively). The pooled correlation between muscle mass on dual-energy X-ray (DXA) or bioelectrical impedance analysis (BIA) and muscle thickness (MT) on ultrasound was moderate (<i>r</i> = 0.56, 95% CI: 0.49–0.62). There was a low-to-moderate correlation between muscle mass on DXA or BIA and cross-sectional area (CSA) on ultrasound (<i>r</i> = 0.267–0.584). The correlation was high to very high between muscle mass from DXA and the ultrasound-predicted formula (<i>r</i> = 0.85–0.963). The CSA from ultrasound had a high or very high correlation with that from computed tomography or magnetic resonance imaging (<i>r</i> = 0.826, intra (inter)-correlation coefficient [ICC] = 0.998–0.999). The respective meta-analyses showed good inter-rater and intra-rater reliabilities (ICC &#x3e; 0.9). <b><i>Conclusion:</i></b> Ultrasonography is a reliable and valid diagnostic method for the quantitative assessment of appendicular muscle mass in sarcopenia in older people. The thickness and CSA of the RF or GM seem to be proper ultrasound parameters to predict muscle mass in sarcopenia. Multicenter studies with large samples and the application of new ultrasonic techniques will be the future research directions.