03INV Idiopathic inflammatory myopathies: current state of the field, new insights and treatment

The idiopathic inflammatory myopathies are a heterogeneous group of acquired diseases comprising dermatomyositis (DM), antisynthetase syndrome, immune-mediated necrotizing myopathy, inclusion body myositis (IBM) and myositis occurring in overlap syndromes with other autoimmune systemic diseases. Drug-induced myositis is increasingly seen in association with treatment with statins or checkpoint inhibitors. International collaboration projects in the last decade resulted in better understanding of the genetic predisposition and etiopathogenetic pathways leading to disease initiation and progression, in development of the new disease classification and treatment response criteria, and in a number of large-scale clinical trials with several biologic or targeted synthetic drugs. The new recommendations for cancer screening in myositis are an important clinical aid. In addition to more refined characterisation of the association with HLA molecules, the relationship of IIM to other non-HLA genes or to low gene copy number of complement has been demonstrated. Further evidence is emerging for an important role of autoantibodies, not only in relation to clinical manifestations and prognosis, but also in terms of a possible pathogenic effect in the disease. Attention is now also being paid to organ involvement in myositis, particularly the lungs, as new therapeutic options for interstitial lung disease became available. Several new clinical trials with biologics have generally failed to demonstrate sufficient efficacy in the treatment of IIM, although there are signals of a possible benefit in some subtypes of IIM. A landmark clinical trial with intravenous immunoglobulins has provided evidence of significant efficacy in patients with DM leading to a new regulatory approval in many years. A number of other clinical trials are currently underway in various subtypes of IIM, including notoriously resistant IBM, with drugs that have very intriguing mechanisms of action and some have already been shown to be effective in similar immune-mediated diseases. Results will be known in the coming months/years.