Ultrasound-based index of sarcopenia and correlation with skeletal muscle mass estimation by biolectrical impedence analysis

Aim: The aim of this study was to introduce a new, ultrasound-based method for diagnosing sarcopenia and test its validity against a conventional, clinically used method based on bioelectrical impedence analysis (BIA)1. Method: 24 participants (13 men and 11 women), aged 65-83 yrs, were recruited for this study. Skeletal Muscle Index (SMI) was estimated by BIA as described by Janssen et al (2002)1. The ultrasound-based evaluation of sarcopenia was obtained from a sagittal image of the vastus lateralis muscle acquired in the lower third of the muscle belly using a linear probe (13-4 MHz) with an Esaote Mylab 25 ultrasound machine. For each ultrasound image, fascicle length (Lf) and muscle thickness (Tm) were measured using the Java-based image analysis software ImageJ (National Institute of Health). Individuals were classified as sarcopenic if the Lf/Tm ratio was > 4.38 corresponding to the cut-off value of 1-SD above the mean of a young adult reference population (Narici et al 2011)2. The data were analysed with descriptive statistics and with the Spearman correlation coefficient. Results: mean BMI was 26.5 (±3.7) in men and 24.7 (±3.5) in women; Skeletal Muscle Index (SMI) was 34.3 (±3.2) in men and 30.8 (±4.9) in women. With the BIA method, a total of 6 individuals were classified as sarcopenic (prevalence of 25%) and 18 individuals as non-sarcopenic and. Using the ultrasound method, 8 individuals were classified as sarcopenic (prevalence of 33%) and 16 as non-sarcopenic. The ultrasound method for diagnosing sarcopenia was found to be significantly correlated with the BIA method (r=0.4, p<0.03), indicating that with decreasing muscle mass, alterations in muscle architecture occur as muscle thickness decreases more than fascicle length, i.e. the higher the Lf/Tm ratio, the greater the sarcopenia. Conclusions The results obtained in the present study show that the ultrasound-based method for diagnosing sarcopenia is, 1) significantly correlated with the widely used BIA-based method, and 2) able to detect a greater prevalence of sarcopenia than the BIA-based method because is muscle-specific. The ‘sarcopenia index’2 obtained by ultrasound thus seems to be a useful biomarker for diagnosing sarcopenia and may represent a useful clinical application. References 1) Janssen I., Heymsfield S., Ross R., Low Relative Skeletal Muscle Mass (Sarcopenia) in Older Persons Is Associated with Functional Impairment and Physical Disability. JAGS 50:889–896, 2002 2) Narici M., Trisolino G., Bracci G. Seynnes et al. Age-related changes in muscle architecture: a signature of sarcopenia. J Muscle Res Cell Motil (2011) 32:327–373