Controversies in geriatric medicine
Sarcopenia: A useful paradigm for physical frailty

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Abstract

The concepts and definitions of frailty and sarcopenia are being actively revised in recent times. The most popular present definitions of sarcopenia and physical frailty share many common points. Both sarcopenia and frailty may be best understood when considered as geriatric syndromes. Geriatric syndromes are relevant because they are usually the presenting manifestation of multiple underlying diseases and conditions; they cause morbidity by themselves; and are only treatable when a multidimensional approach is used. Frailty can be well understood as a geriatric syndrome. The risk of frailty increases with age and with the accumulated effects of multiple conditions and predisposing factors, and subjects identified as frail have impaired outcomes. Sarcopenia is also best understood as a geriatric syndrome. Frailty is a complex problem that includes physical, functional, mental and social aspects. Physical frailty has close links to muscle function, and therefore to the new definitions of sarcopenia. Many of the adverse outcomes of frailty are probably mediated by sarcopenia. Sarcopenia can be considered as being a key pathway between frailty and disability. Although frailty affects both musculoskeletal and non-musculoskeletal systems, sarcopenia constitutes one of the main components of the clinical frailty syndrome. The concept of sarcopenia being closer to the musculoskeletal system (the organ system with the function of mobility), we propose that sarcopenia, using recent definitions and considered as a geriatric syndrome, is a more useful paradigm and one that may be easier to put into operational definitions than physical frailty for clinical prevention, diagnosis and intervention. Diagnostic criteria for sarcopenia may be used to measure physical frailty in research and practice.

Introduction

The concepts and definitions of frailty and sarcopenia are being actively revised in recent times [1], [2], [3]. Initial definitions of frailty considered it as a synonymous of disability, multimorbidity or extreme old age, being only a subjective perception by the clinician [4]. During the last decade the concept of frailty started to approach some consensus: frailty is a biological syndrome of decreased reserve and resistance to stressors, resulting from cumulative declines across multiple physiologic systems and causing vulnerability to adverse outcomes [5]. However, this concept has proved elusive when it is brought to clinical practice. Frailty is a complex and multidimensional construct, which explains the problems involved in its working definition and operationalization in clinical research and practice [6]. Current thinking is that frailty cannot be limited to a physical paradigm; psychological, cognitive, emotional, social and spiritual factors contribute to frailty and need to be taken into account in its definition [1].

Research on physical frailty is far more advanced than research on other aspects of frailty. A phenotypical approach to physical frailty has been introduced in clinical practice [5], although it has not shown full success in the prediction of outcomes [7], [8]. An alternative model of accumulation of deficits has also been used [9], [10]. None of these approaches seem to yield similar results in clinical practice [11], which is again confusing to our present understanding of physical frailty. What do these indicators of frailty really measure?

Physical frailty is strongly linked to muscle mass and function. In 1988, Irwin H. Rosenberg stated that “over the decades of life, there is probably no decline in structure and function more dramatic than the decline in lean body mass or muscle mass” [12]. He postulated that this decline has a negative impact on ambulation, mobility, breathing, energy intake, overall nutrient intake and status and independence. He suggested giving it a name: sarcopenia. The definition of sarcopenia has also been evolving since it was named, starting from muscle mass and moving toward muscle strength and function, physical performance and impaired outcomes [2], [13], [14]. One of the most recent definitions states that sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes, such as physical disability, poor quality of life and death [14]. Many would argue that the whole picture depicted here for sarcopenia is not far from the current phenotypic definition of frailty.

A careful examination of the most popular present definitions of sarcopenia and physical frailty shows that they share many common points. For instance, three out of five elements of Fried's phenotypical definition of physical frailty (shrinking, weakness, slowness) [5] are part of the EWGSOP definition of sarcopenia [14]. However, from a physiological and clinical perspective, sarcopenia is closer to an organ function (skeletal muscle) than frailty, and may be easier to apply in clinical practice. Drug regulatory agencies consider frailty a problematic indication for drug approval [15] and may find sarcopenia (broadly viewed as “muscle insufficiency”, which is closer to most organs and system disease pathways) a simpler construct.

In this paper, we will review how the concept of geriatric syndromes has changed, we will explore some syndromic approaches to frailty and sarcopenia, and we will argue that sarcopenia is the major determinant of physical frailty. We will, thus, propose that sarcopenia is a useful paradigm for physical frailty.

Section snippets

The evolving concept of geriatric syndromes

One of the problems that are complicating the development and validation of the concepts of frailty and sarcopenia is that both need to be distinguished from normal age-related changes and from other age-related diseases and conditions. In fact, recent literature shows that both sarcopenia and frailty may be best understood when considered as geriatric syndromes [16], [17], [18].

The term “geriatric syndrome” has been commonly used in the geriatric literature for decades to define complex

A syndromic approach to sarcopenia and frailty

Being said that, frailty can be well understood as a geriatric syndrome. Frailty, and even isolated physical frailty, does not seem to fit into a single disease category, or to be only usual ageing. In specific life environments/conditions, it can be the consequence of a single disease and of multimorbid conditions [22]. It can be identified or defined by observing or measuring different clinical features, being the clinical manifestation of multiple underlying diseases and complex conditions.

Sarcopenia, the major determinant of physical frailty

Older definitions of sarcopenia, based only on absolute or relative muscle mass, are losing relevance, as it is now clear that muscle mass, strength and function do not run parallel. The concept of frailty developed in this arena, pointing out that functional aspects were more relevantly linked to relevant health outcomes than muscle mass [34]. However, new definitions of sarcopenia have moved away from the “muscle mass only” concept to include muscle function and physical performance.

As

Disclosure of interest

The authors have not supplied their declaration of conflict of interest.

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