Rheumatoid sarcopenia: loss of skeletal muscle strength and mass in rheumatoid arthritis.

Sarcopenia, a disorder that involves the generalized loss of skeletal muscle strength and mass, was formally recognized as a disease by its inclusion in the International Classification of Diseases in 2016. Sarcopenia typically affects older people, but younger individuals with chronic disease are also at risk. The risk of sarcopenia is high (with a prevalence of ≥25%) in individuals with rheumatoid arthritis (RA), and this rheumatoid sarcopenia is associated with increased likelihood of falls, fractures and physical disability, in addition to the burden of joint inflammation and damage. Chronic inflammation mediated by cytokines such as TNF, IL-6 and IFNγ contributes to aberrant muscle homeostasis (for instance, by exacerbating muscle protein breakdown), and results from transcriptomic studies have identified dysfunction of muscle stem cells and metabolism in RA. Progressive resistance exercise is an effective therapy for rheumatoid sarcopenia but it can be challenging or unsuitable for some individuals. The unmet need for anti-sarcopenia pharmacotherapies is great, both for people with RA and for otherwise healthy older adults. Sarcopenia, which involves the generalized loss of skeletal muscle strength and mass, is commonly associated with rheumatoid arthritis. In this Review, the authors discuss the epidemiology, pathophysiology and identification of rheumatoid sarcopenia and present evidence for the therapeutic roles of physical activity, nutrition and pharmacotherapy. Key points: Sarcopenia is a progressive and generalized skeletal muscle disorder that involves the accelerated loss of muscle strength and mass and affects approximately one in four people with rheumatoid arthritis (RA). Disease-specific risk factors for rheumatoid sarcopenia include high disease activity, raised inflammatory markers, long disease duration, rheumatoid factor positivity, glucocorticoid use and joint damage. Inflammatory cytokines can accelerate the development of sarcopenia through elevation of muscle proteolysis, disruption of muscle stem cell self-renewal and direct impairment of myofibre force. Muscle strength is the key marker of sarcopenia; handgrip strength can be measured in RA and specific devices are available for individuals with severe hand arthritis. Muscle mass in RA is most frequently measured with dual-energy X-ray absorptiometry, although newer techniques (ultrasonography, CT and MRI) are emerging, and panels of molecular biomarkers might prove useful in the future. Exercise is currently the most effective intervention for improving strength and muscle mass in people with RA. [ABSTRACT FROM AUTHOR]