[Recent research developments in polymyositis/dermatomyositis]

The idiopathic inflammatory myopathies, polymyositis (PM) and dermatomyositis (DM), are evaluated as systemic autoimmune diseases without the pathology determined. Past immunohistochemical findings suggested that the effector response is driven predominantly by CD4 T cells and by humoral immunity in DM, and by cytotoxic T cells in PM. However, histological observations of muscle tissue do not necessarily distinguish DM and PM. Thus, the two diseases including amyopathic DM might represent a spectrum of illness in which some patients suffer only from a muscle disease or from a skin disease. In comparison with research studies on other rheumatic diseases, there are much fewer research studies conducted on PM/DM. The relationship between PM and DM is not clear yet. We reviewed past clinical and basic research on the pathology of PM/DM, including research on relevant T cells, B cells and cytokines.