Idiopathic inflammatory myopathies (IIM), collectively known as
myositis, are a composite group of rare
autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of
myositis is subacute, progressive, symmetrical
muscle weakness in the proximal arms and legs, whereas subtypes of
myositis may also present with extramuscular features, such as skin involvement,
arthritis or
interstitial lung disease (ILD). Established subgroups of IIM include
dermatomyositis (DM), immune-mediated necrotizing
myopathy (IMNM), anti-
synthetase syndrome (ASyS), overlap
myositis (OM) and
inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of
glucocorticoids and other immunosuppressive or
immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of
myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.