sarcopenia. To do this we have assembled a wide range of authors from around the world, who are experts in this topic area. We also focus on primary and secondary prevention of sarcopenia as important approaches to enhance the quality of life in older persons.
This book represents a state‐of‐the‐art textbook, with a comprehensive approach to sarcopenia. We hope it will be a valuable reference tool to all those who are interested in this topic. Our authors have taken complex topics and written about them in a clear way allowing access to the knowledge for those starting out in the field, as well as expert researchers and clinicians who are interested in recognizing and treating sarcopenia.
Alfonso J. Cruz‐Jentoft and John E. Morley
CHAPTER 1 Definitions of Sarcopenia
Alfonso J. Cruz‐Jentoft1, Beatriz Montero‐Errasquín2, and John E. Morley3
1 Servicio de Geriatría, Hospital Universitario Ramón y Cajal (IRYCIS), Universidad Europea de Madrid, Madrid, Spain
2 Servicio de Geriatría, Hospital Universitario Ramón y Cajal (IRYCIS), Madrid, Spain
3 Division of Geriatric Medicine, Saint Louis University School of Medicine, St. Louis, MO, USA
SARCOPENIA: BIRTH AND FIRST STEPS
Irving Rosenberg is credited to have coined the term sarcopenia (from the Greek roots – sarx = flesh and ‐penia = low, meaning “poverty of flesh”) in 1988 to describe the striking age‐related decline in lean body mass and its potential functional significance [1].
Methods to estimate muscle mass (or lean body mass) were increasingly available, as were epidemiological studies using such techniques. Based on these parameters, sarcopenia was operationally defined as a gradual loss of muscle mass. For instance, Baumgartner used a definition based on appendicular skeletal muscle mass estimated by dual‐energy x‐ray absorptiometry (DXA), corrected for height, and defined sarcopenia as being two standard deviations below sex‐specific means of healthy young persons (18–40 years) of a reference population [2]. Longitudinal studies confirmed that a progressive reduction in muscle mass was present in both males and females [3]. Muscle mass declines at approximately 1–2% per year after the age of 50 years. Sarcopenia, when defined as a severe muscle mass loss (two standard deviations below healthy young populations), is present in 5–13% of persons of 60–70 years old and 11–50% of those over 80 years [4].
While the definition of sarcopenia based on a reduced muscle mass alone served the scientific community fairly well, it was less satisfying for clinicians, the pharmaceutical industry, and regulatory agencies. Unlike bone mineral density, measures of muscle mass have not been widely adopted by clinicians. Regulatory agencies have failed to accept that restoration of muscle mass is a valid reason to allow a drug to be approved for use. Also, many crucial aspects of sarcopenia are missed by the simplistic use of muscle mass as a measure, which has shown to be a weak predictor of outcomes; and the link between muscle mass, muscle function (defined by muscle strength and power), physical performance, and other downstream outcomes is not linear [5–8]. The fact that all clinical measures of muscle mass are in fact estimations and have a wide range of measurement error may partially explain this situation [9]. Research has also showed that loss of muscle strength is two to five times faster than loss of muscle mass and is associated with changes in muscle quality (defined as intramuscular fat) and is more predictive of outcomes [3, 8].
GROWTH AND ADOLESCENCE OF SARCOPENIA
In the first decade of the twenty‐first century, the relevance of muscle function was so clear that different lines of action were proposed, including the use of different terms to name the condition. Dynapenia and kratopenia were suggested as alternative terms to describe the loss of muscle strength and power [8, 10], and myopenia as an alternative for universal skeletal muscle wasting [11]. However, six different international consensus definitions published at the end of the decade all proposed redefining sarcopenia by adding the loss of muscle mass to the loss of muscle function, with slightly different approaches [10, 12–16].
European Working Group on Sarcopenia in Older People and Asian Working Group on Sarcopenia
To date, this is the most widely cited definition and the only definition that was endorsed by a range of international scientific societies (European Geriatric Medicine Society [EuGMS], European Society for Clinical Nutrition and Metabolism [ESPEN], International Association of Geriatrics and Gerontology‐European Region [IAGG‐ER], International Academy on Nutrition and Aging [IANA]) [13]. The European Working Group on Sarcopenia in Older People (EWGSOP) defined sarcopenia as a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength, with a risk of adverse outcomes such as physical disability, decreased quality of life, and increased mortality. According to the EWGSOP criteria, diagnosis of sarcopenia required documentation of low muscle mass plus documentation of either low muscle strength or low physical performance. With the aim of encouraging the assessment of sarcopenia in all patients and all health‐care settings, the EWGSOP provided a wide range of tools that made the assessment feasible even in settings with limited resources, including a suggested algorithm for case finding based on physical performance (usual gait speed) as the easiest and most reliable first step to begin sarcopenia screening in clinical practice. However, the EWGSOP found no evidence to recommend cut‐off points for each of the parameters used in the definition. The EWGSOP also suggested dividing sarcopenia into categories (primary or age‐related and secondary sarcopenia), and sarcopenia staging to reflect the severity of the condition.
The EWGSOP initiative was strongly supported by the Asian Working Group on Sarcopenia (AWGS) [15]. This group collected the best available evidence of sarcopenia research from Asian countries to establish the consensus for sarcopenia diagnosis and take an extra step forward by proposing gender‐specific cut‐off values for muscle mass estimation with DXA or bioimpedance analysis, handgrip strength, and usual gait speed. In addition to sarcopenia screening for community‐dwelling older people, the AWGS recommended sarcopenia assessment in certain clinical conditions and health‐care settings to facilitate implementing sarcopenia in clinical practice.
European Society for Clinical Nutrition and Metabolism Special Interest Groups
A special interest group on cachexia–anorexia in chronic wasting diseases was created in ESPEN, and the definition, assessment, and staging of cachexia were identified as a priority [12]. In the first consensus paper published by this group on the definition of cachexia and pre‐cachexia, the need of criteria for the differentiation between cachexia and other conditions associated with low muscle mass lead to a cooperation with the ESPEN special interest group on nutrition in geriatrics. Diagnosis of sarcopenia was defined by the combined presence of a low muscle mass (a percentage of muscle mass ≥2 standard deviations below the mean measured in young adults of the National Health and Nutrition Examination Survey [NHANES] population) and low gait speed.
Society for Sarcopenia, Cachexia and Wasting Disorders (SSCWD)
This organization conveyed American and European researchers to develop a definition of sarcopenia that could be a meaningful surrogate for clinically useful endpoints, allow for treatments, include only measurements longitudinally linked to meaningful outcomes, and have definable cut‐off points based on the data [10]. Deviating from the other groups, it was decided that “sarcopenia with limited mobility” would be the preferred term to define persons with a need for therapeutic interventions. Sarcopenia with limited mobility was defined as a muscle loss associated with a slow walking speed, with an approach that mirrored that proposed by ESPEN. The limitation in mobility should not be clearly attributable to the direct effect of specific diseases such as peripheral