Age-related alterations in muscle architecture are a signature of sarcopenia: the ultrasound sarcopenia index

Narici, M ORCID: https://orcid.org/0000-0003-0167-1845, McPhee, J ORCID: https://orcid.org/0000-0002-3659-0773, Conte, M ORCID: https://orcid.org/0000-0002-4621-9898, Franchi, MV ORCID: https://orcid.org/0000-0003-3165-4536, Mitchell, K, Tagliaferri, S ORCID: https://orcid.org/0000-0002-0468-4863, Monti, E ORCID: https://orcid.org/0000-0002-3767-0855, Marcolin, G ORCID: https://orcid.org/0000-0002-2768-3257, Atherton, PJ ORCID: https://orcid.org/0000-0002-7286-046X, Smith, K ORCID: https://orcid.org/0000-0001-8971-6635, Phillips, B ORCID: https://orcid.org/0000-0002-1430-1870, Lund, J ORCID: https://orcid.org/0000-0001-5195-2181, Franceschi, C ORCID: https://orcid.org/0000-0001-9841-6386, Maggio, M ORCID: https://orcid.org/0000-0002-1727-6797 and Butler-Browne, GS ORCID: https://orcid.org/0000-0002-3431-242X (2021) Age-related alterations in muscle architecture are a signature of sarcopenia: the ultrasound sarcopenia index. Journal of Cachexia, Sarcopenia and Muscle, 12 (4). pp. 973-982. ISSN 2190-5991

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Abstract

Background: The assessment of muscle mass is a key determinant of the diagnosis of sarcopenia. We introduce for the first time an ultrasound imaging method for diagnosing sarcopenia based on changes in muscle geometric proportions. Methods: Vastus lateralis muscle fascicle length (Lf) and thickness (Tm) were measured at 35% distal femur length by ultrasonography in a population of 279 individuals classified as moderately active elderly (MAE), sedentary elderly (SE) (n = 109), mobility impaired elderly (MIE) (n = 43), and in adult young controls (YC) (n = 60). The ratio of Lf/Tm was calculated to obtain an ultrasound index of the loss of muscle mass associated with sarcopenia (USI). In a subsample of elderly male individuals (n = 76) in which corresponding DXA measurements were available (MAE, n = 52 and SE, n = 24), DXA-derived skeletal muscle index (SMI, appendicular limb mass/height2) was compared with corresponding USI values. Results: For both young and older participants, USI values were found to be independent of sex, height and body mass. USI values were 3.70 ± 0.52 for YC, 4.50 ± 0.72 for the MAE, 5.05 ± 1.11 for the SE and 6.31 ± 1.38 for the MIE, all significantly different between each other (P < 0.0001). Based on the USI Z-scores, with reference to the YC population, the 219 elderly participants were stratified according to their muscle sarcopenic status. Individuals with USI values within a range of 3.70 < USI ≥ 4.23 were classified as non-sarcopenic (prevalence 23.7%), those with USI values within 4.23 < USI ≥ 4.76 were classified as pre-sarcopenic (prevalence 23.7%), those with USI values within 4.76 < USI ≥ 5.29 were classified as moderately sarcopenic (prevalence 15.1%), those with USI values within range 5.29 < USI ≥ 5.82 were classified as sarcopenic (prevalence 27.9%), and those with USI values >5.82 were classified as severely sarcopenic (prevalence 9.6%). The DXA-derived SMI was found to be significantly correlated with USI (r = 0.61, P < 0.0001). Notably, the USI cut-off value for moderate sarcopenia (4.76 a.u.) was found to coincide with the DXA cut-off value of sarcopenia (7.26 kg/m2). Conclusions: We propose a novel, practical, and inexpensive imaging marker of the loss of muscle mass associated with sarcopenia, called the ultrasound sarcopenic index (USI), based on changes in muscle geometric proportions. These changes provide a useful ‘signature of sarcopenia’ and allow the stratification of individuals according to the presence and severity of muscle sarcopenia. We are convinced that the USI will be a useful clinical tool for confirming the diagnosis of sarcopenia, of which the assessment of muscle mass is a key-component.