Sarcopenia-2021 Pathophysiology, Diagnosis, Therapy

Sarcopenia is a progressive, generalized skeletal muscle disease with the loss of muscle mass and function, associated with adverse outcomes and poor prognosis. Sarcopenia first was regarded as an age-related disorder of older people (primary sarcopenia). Later it turned out that it can also occur in young age due to a range of chronic disorders such as cancer, anorexia or malnutrition (secondary sarcopenia). This paper overviews the pathophysiology of sarcopenia and the factors involved in the muscle mass loss, i.e., physical inactivity, insulin resistance, low-grade chronic inflammation, hepatokines and myokines. The basic feature is the imbalance between proteolysis and protein synthesis that leads to muscle atrophy. We discuss the relationship between liver, muscle and adipose tissue in non-alcoholic fatty liver disease and cirrhosis. To diagnose sarcopenia, there are a range of tests and tools that measure muscle strength and muscle mass as well as physical performance. The low muscle strength (hand grip strength) is the primary parameter of the diagnosis, the best measure of muscle function. The loss of skeletal muscle mass assessed by dual-energy X-ray absorptiometry, bioelectric impedance analysis, computer tomography, or magnetic resonance imaging confirms diagnosis, while the decrease in physical performance reflects severe sarcopenia. For the treatment and prevention of progression, the most important is the regular physical activity started from early adulthood, and healthy diet containing protein-calorie hyperalimentation. In addition, a pharmacotherapy with the supplementation of vitamin D and testosterone, furthermore, the administration of L-carnitine and branched-chain amino acids can be recommended. In the case of secondary sarcopenia, the underlying disease also requires treatment.