Clinical outcomes related to muscle mass in humans with cancer and catabolic illnesses.

It is generally accepted that excessive loss of skeletal muscle mass is detrimental. Depletion of muscle mass is associated with poor prognosis in diabetes, trauma, sepsis, lung disease, renal failure and heart failure. In this review we discuss the emergence of muscle mass measurement using diagnostic imaging and the relationship between muscle mass and clinical outcome. The pursuit of specific biochemical targets for reversal of muscle wasting, has spawned a host of investigator initiated research on muscle wasting as well as investigational new drug programs in pharmaceutical companies. Research on therapeutics targeting muscle is to a large extent done in animal models, with relatively few investigations done using human muscle or reporting upon muscle mass or muscle-related outcomes in humans. Since ∼1990, a quantitative approach, as opposed to a purely functional approach, to muscle atrophy and hypertrophy has become accessible with the advent of image-based assessments (dual energy X-ray absorptiometry, computed tomography and magnetic resonance imaging). These methods have high specificity and precision. In conclusion, current imaging techniques allow us to quantify the degree of muscularity of different individuals, to relate muscle mass to disease-specific outcomes, to define sarcopenia [severe muscle depletion] in quantitative terms, to detect the prevalence and rates of catabolic loss of muscle, the behavior of specific individual muscles and to define the efficacy of different therapies developed for the treatment of muscle wasting. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.