Estimating site-specific muscle loss: a valuable tool for early sarcopenia detection?

Currently, sarcopenia is commonly diagnosed using the appendicular lean mass calculation derived from the dual-energy X-ray absorptiometry (DXA) estimate. However, the DXA estimate of lean mass only gives a regional estimate of body composition and cannot differentiate different muscle groups. In contrast, diagnostic B-mode ultrasound can provide reliable estimates of individual muscle groups and may provide a method for earlier detection of sarcopenia. This may be important because it appears that the loss of skeletal muscle with age appears pronounced in certain muscle groups of the lower leg, while only minimally affecting others. This has been demonstrated in several large cross-sectional studies as well as a longitudinal investigation. In addition, this site-specific loss of muscle mass is associated with declines in muscle performance. We wish to suggest that the ultrasound estimate of muscle thickness may be a useful measurement to include when quantifying the age-related loss of muscle mass. Although the DXA is commonly used, changes in the anterior portion of the thigh may be occurring but may not necessarily be detected by the DXA estimate. This site-specific estimate coupled with a measure of muscle strength/performance may provide clinicians with a more complete picture of muscular changes with age.