Sarcopenia

Sarcopenia

Sarcopenia, derived from the Greek words σάρξ (sarx) for "flesh" and πενία (penia) for "poverty," is the degenerative loss of skeletal muscle mass, quality, and strength associated with aging. This condition is a significant factor in the frailty syndrome and can occur independently or as a component of cachexia, the latter of which includes systemic inflammation and is often secondary to chronic diseases such as cancer. Unlike cachexia, sarcopenia can develop in otherwise healthy individuals without the presence of malaise.

Signs and Symptoms

Sarcopenia is primarily characterized by muscle atrophy, a decrease in the size of the muscle, leading to a reduction in muscle tissue quality. This decline is marked by fat infiltration, increased fibrosis, alterations in muscle metabolism, oxidative stress, and the degeneration of the neuromuscular junction. These changes result in a progressive loss of muscle function and increased frailty. The condition is influenced by the initial amount of muscle mass and the rate at which aging reduces this mass. Notably, the impact of sarcopenia on independence varies among individuals, with severe muscle wasting representing a disease threshold that is pathologically distinct for each person.

Muscle atrophy in sarcopenia also involves a reduction in the circumference of muscle fibers, particularly noticeable in type II fibers, with less impact on type I fibers. This process includes the conversion of denervated type II fibers into type I fibers through reinnervation by slow type I fiber motor nerves.

Causes

Sarcopenia's development is multifactorial, involving diminished anabolic signals, like growth hormone and testosterone, alongside the promotion of catabolic signals, such as pro-inflammatory cytokines. The condition is partly attributed to a failure in the activation of satellite cells, which are essential for muscle regeneration following injury or exercise. Aging also leads to an accumulation of oxidized proteins within muscle tissue, contributing to muscle strength decline. Additionally, evolutionary theories suggest that modern sedentary lifestyles are mismatched with genetic parameters selected for a high level of muscular effort in the Paleolithic era. Early environmental influences, indicated by markers such as low birth weight, have been associated with reduced muscle mass and strength in later life.

Diagnosis

The diagnosis of sarcopenia has evolved since its initial definition by Baumgartner et al. in 1998, which relied on lean body mass measurements via dual-energy X-ray absorptiometry (DEXA) against a reference population. Current consensus, including criteria from the European Working Group on Sarcopenia in Older People (EWGSOP), considers low muscle mass and either low gait speed or muscular strength as diagnostic criteria. Severe sarcopenia is diagnosed when all three conditions are present.

Classification

Sarcopenia is classified under the ICD-10-CM code M62.84 in the United States, reflecting its recognition as a distinct medical condition. The EWGSOP has also provided a clinical definition and diagnostic criteria focused on the presence of low muscle mass, muscular strength, or physical performance.

Management

Exercise, particularly resistance training, is considered a key intervention for sarcopenia, capable of improving muscle mass, strength, and physical performance. However, the translation of exercise benefits into clinical practice remains challenging due to variability in exercise prescriptions. While no medications are specifically approved for sarcopenia, supplements like β-hydroxy β-methylbutyrate (HMB) have shown promise in preventing muscle mass loss. Nutritional strategies, including increased protein intake and key nutrient supplementation, are also recommended to support muscle health in older adults.

Epidemiology

Sarcopenia's prevalence varies, with studies indicating rates of 4.6% to 36.5% in older adults, depending on the diagnostic criteria used. The condition affects approximately half of individuals over 80, highlighting its significance as a public health concern.

Society and Culture

With increasing longevity and reduced physical activity in industrialized societies, sarcopenia poses a growing challenge. It significantly impacts the ability of the elderly to live independently and is a predictor of disability, poor balance, falls, and fractures. Sarcopenia, alongside osteoporosis, contributes to the frailty often observed in the elderly population.

Research Directions

Future research aims to refine diagnostic criteria, understand the molecular mechanisms underlying sarcopenia, and explore effective interventions. Studies are also focused on integrating lifestyle factors, such as exercise and nutrition, into prevention and treatment strategies.

Novartis proposes the use of a new molecule BYM338 Bimagrumab for treatment of sarcopenia and plans to make a FDA submission in 2019.\

Clinical practice

Diagnosis can be difficult due to the comprehensive measurements used in research that are not always practical in healthcare settings. Hand grip strength alone has also been advocated as a clinical marker of sarcopenia that is simple and cost effective and has good predictive power, although it does not provide comprehensive information.

See also

• Sarcopenic obesity

Sarcopenia Resources
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