Cachexia in rheumatoid arthritis

• Published in: International journal of cardiology 2002-09, Vol.85 (1), p.89-99
• Main Authors: Walsmith, Joseph, Roubenoff, Ronenn
• Format: Article
• Language: English
• Subjects: Arthritis, Rheumatoid - complications; Arthritis, Rheumatoid - diagnosis; Cachexia; Cachexia - diagnosis; Cachexia - etiology; Exercise; Humans; Insulin action; Interleukin-1β; Physical activity; Protein metabolism; Rheumatoid arthritis; Tumor necrosis factor-α
• ISSN: 0167-5273; 1874-1754
• DOI: 10.1016/S0167-5273(02)00237-1

Rheumatoid arthritis is a debilitating, chronic, systemic, autoimmune disease of unknown etiology that causes destruction of joint cartilage and bone. It generally occurs between the fourth and sixth decades of life, and affects two to three times more women than men. It is characterized by joint stiffness, pain, and swelling, and is accompanied by a loss of body cell mass. This loss of cell mass, known as rheumatoid cachexia, predominates in skeletal muscle, but also occurs in the viscera and immune system. Thus, rheumatoid cachexia leads to muscle weakness and a loss of functional capacity, and is believed to accelerate morbidity and mortality in rheumatoid arthritis. Currently there is no established mechanism for rheumatoid cachexia, but it is accompanied by elevated resting energy expenditure, accelerated whole-body protein catabolism, and excess production of the inflammatory cytokines, tumor necrosis factor-α and interleukin-1β. Tumor necrosis factor-α is probably the central mediator of muscle wasting in rheumatoid arthritis, and is known to act synergistically with interleukin-1β to promote cachexia. In general, tumor necrosis factor-α and interleukin-1β are thought to alter the balance between protein degradation and protein synthesis in rheumatoid arthritis to cause muscle wasting. The precise mechanism by which they do this is not known. Reduced peripheral insulin action and low habitual physical activity are important consequences of rheumatoid arthritis, and have also been implicated as mediators of rheumatoid cachexia. Insulin inhibits muscle protein degradation. Consequently, reduced peripheral insulin action in rheumatoid arthritis is thought to be permissive to cytokine-driven muscle loss. The cause of reduced peripheral insulin action in rheumatoid arthritis is not known, but tumor necrosis factor-α has been shown to interfere with insulin receptor signaling and is probably an important contributor. Low habitual physical activity has consistently been observed in rheumatoid arthritis and is an important consequence of, and contributor to, muscle wasting. In addition, low physical activity predisposes to fat gain and is believed to precipitate a negative reinforcing cycle of muscle loss, reduced physical function, and fat gain in rheumatoid arthritis, which leads to ‘cachectic obesity’. To date, there is no standard treatment for rheumatoid cachexia. However, physical exercise is currently believed to be the most important and clinically