The pathogenesis of dermatomyositis

Abstract

Dermatomyositis is an unusual condition with a characteristic rash and inflammation of the muscles, which can lead to severe weakness and sometimes problems with breathing and swallowing. In this study, the authors, based in Cardiff, Wales, review what is known about the causes of this potentially serious disease. Like other autoimmune conditions, dermatomyositis is thought to be due to a combination of genetic and environmental factors. Several genes (e.g. HLA class B alleles) have been linked with dermatomyositis, and specific genes are closely linked with the production of unique antibodies which are in turn linked to specific types of the condition. Several environmental factors can trigger the development of dermatomyositis. These include ultraviolet light, vitamin D deficiency, infection and underlying cancer (particularly in the elderly). Drugs, notably statins, can induce myositis (muscle inflammation) and systemic steroids can induce muscle weakness, but symptoms typically improve on reducing the drug. Various immune factors are involved in dermatomyositis. Biopsies of muscles show inflammation, with large numbers of T cells called lymphocytes and macrophages which cause tissue damage. Additionally, some auto-antibodies appear to target the muscles, also damaging muscle cells. There are increased blood levels of several cytokines (molecules such as TNFα) which also provoke inflammation. Thus, many different genetic and environmental factors together can trigger the development of dermatomyositis.