Determination of Skeletal Muscle Mass Index Values in the Turkish Population Using Dual Energy X-Ray Absorptiometry

Overview

Sarcopenia is defined by the European Working Group on Sarcopenia in Older People (EWGSOP) as "a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength, carrying a risk of adverse outcomes such as physical disability, fractures, falls, impaired quality of life, and death." However, despite the severity of the disease, a single diagnostic criterion has not yet been established, and various guidelines have been proposed to standardize the diagnostic criteria and cut-off values. Current European Working Group on Sarcopenia in Older People (EWGSOP) recommendations focus on European populations and, where possible, the use of normative references from healthy young adults. Since measurements such as gait and muscle strength are height-dependent, the use of regional normative populations is recommended whenever possible. Currently, some cut-off points for the diagnosis of sarcopenia are arbitrary. The development of validated cut-off points will depend on normative data and their predictive value for endpoints. Further studies are needed to determine whether gender-specific and region-specific threshold values for the diagnosis of sarcopenia improve the prediction of sarcopenia outcomes. There are no studies in the literature on dual-energy x-ray absorptiometry cutoff values specific to the Turkish population. In our study, we aimed to define reference cutoff values for muscle mass, muscle strength, and calf circumference in Türkiye in order to improve the general applicability of EWGSOP criteria.

When low muscle strength is detected, the patient is evaluated for possible sarcopenia; the diagnosis is confirmed by the presence of low muscle mass or quality. Severe sarcopenia is considered when low muscle strength, low muscle mass or quality are accompanied by low physical performance. Muscle strength can be assessed by measuring hand grip strength and isometric or isokinetic measurements of lower extremity strength. A wide variety of techniques are used to measure muscle mass, including magnetic resonance imaging (MRI), computed tomography (CT), dual-energy x-ray absorptiometry (DEXA), bioelectrical impedance analysis (BIA), and anthropometric measurements; the most suitable method should be determined based on cost, accessibility, and ease of use. Muscle mass is related to body size; that is, individuals with larger body sizes typically have greater muscle mass. Therefore, to adjust for body size, the skeletal muscle index (SMI) is calculated as appendicular skeletal muscle mass (ALM) / height² (m²). The SMI cut-off value for sarcopenia, as defined by EWGSOP2, is \<5.5 kg/m² for women and \<7.0 kg/m² for men. There is ongoing debate regarding the preferred adjustment and whether the same method can be used for all populations. Physical performance assessment can be measured in various ways, including walking speed, the Short Physical Performance Battery (SPPB), and the Timed Up and Go Test (TUG).