Reply to sarcopenia is more than simply documenting low skeletal muscle mass

We thank Dr. Clintosun and colleagues for their interest in our study.1 They are accurate in pointing out that the European Working Group on Sarcopenia in Older People (EWGSOP) defined sarcopenia as a loss of muscle mass and low muscle strength or low physical performance.2 The lack of information regarding strength and performance is an acknowledged limitation of our study. Yet one would expect that if some patients with low muscle mass and preserved muscle function were inappropriately classified as sarcopenic in our study, the effect would be even greater than we determined. Furthermore, multiple definitions of the term “sarcopenia” remain in use in the literature. Although many contain criteria involving strength and performance in addition to muscle mass, the use of sarcopenia is not uniform. It is important to note that both younger patients and those with internal malignancies were not specifically targeted by the EWGSOP. Indeed, an international consensus group met to define and classify cancer cachexia. They defined sarcopenic muscle mass as appendicular muscle mass of <7.26 kg/m2 in men and 5.45 kg/m2 in women,3 which is the definition used in our study.1 This finding was validated in a recent international multicenter study4 and in a number of retrospective studies. Accordingly, criteria consistent with sarcopenia have been defined as low appendicular skeletal muscle mass relative to height, low muscle strength, and/or low physical performance.5 This definition of sarcopenia has been used successfully to identify risk in a number of human malignancies. Finally, we would disagree that analysis of a single-slice computed tomography scan at L3 is not an appropriate technique with which to assess skeletal muscle mass. This technique has been validated and used in numerous previous studies to assess muscle mass and predict outcomes. Indeed, the EWGSOP and others characterize both computed tomography and dual-energy x-ray absorptiometry as preferred alternatives for the assessment of muscle mass. No specific funding was disclosed. The authors made no disclosures. Matthew K. Tollefson, MD Sarah P. Psutka, MD Department of Urology Mayo Clinic Rochester, Minnesota