Internal medicine

Pathology

Inclusion body myositis

Disease

Antibody

Autoantibody

Immunology

Myopathy

Interstitial lung disease

Lung

Arthritis

Dermatomyositis

Polymyositis

Myositis

Medicine

Nature Reviews Rheumatology

The idiopathic inflammatory myopathies are a group of disorders that involve inflammation of skeletal muscles and extramuscular manifestations. New classification criteria capture a broad range of these disorders but should be further defined in the future to incorporate new data. The idiopathic inflammatory myopathies (IIMs; also known as myositis) are a heterogeneous group of disorders in which a common feature is chronic inflammation of skeletal muscle, leading to muscle weakness. Other organs are frequently affected in IIMs, such as the skin, joints, lungs, gastrointestinal tract and heart, contributing to morbidity and mortality. Currently, IIMs are most often subclassified into polymyositis, dermatomyositis and inclusion body myositis, but this subclassification has limitations as these subgroups often have overlapping clinical and histopathological features, and outcomes vary within the subgroups; additionally, subgroups without considerable myopathy are not included. A new way of subgrouping patients could be on the basis of the presence of myositis-specific autoantibodies. These autoantibodies are associated with distinct clinical features and, moreover, can help to identify subsets of IIMs in which extramuscular symptoms, such as skin manifestations, arthritis or interstitial lung disease, might be the presenting or predominant feature when muscle symptoms are mild or absent. The recognition that subphenotypes with single-organ involvement other than muscles exist is important for identifying patients with early disease, for clinical care demanding team management and in designing clinical studies to improve our understanding of this heterogeneous disease to develop new therapies.

Classification of myositis