炎症性筋疾患の診断と治療：update 2021

抄録

Idiopathic inflammatory myopathies (IIMs) are a group of disorders complicated by inflammation and resultant damage of skeletal muscles without known causes. Major advances have been recently made in the field of IIMs, including new classification criteria to better identify the patients with IIMs, and discovery of detailed muscle pathologic features and myositis–specific and myositis–associated autoantibodies that facilitates subgrouping of patients into more specific clinical phenotypes. IIMs are now classified into four major subgroups, i.e., dermatomyositis (DM), anti–synthetase syndrome (ASSD), immune–mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). Patients with concomitant features of other connective tissue diseases are considered overlap syndrome. Almost all patients who used to be diagnosed as having ‘polymyositis’ are now re–classified as IBM, IMNM, or ASSD. IIMs are originally characterized by the presence of myositis, but it has been recently recognized that patients with typical DM rashes or myositis–specific autoantibodies plus interstitial lung disease without apparent skeletal muscle involvement are also included in this spectrum. Recent studies evaluating immunophenotypes of individual IIM subgroups have shown distinct pathophysiologies : type I interferonopathy and activation of the complement system in DM, type II interferon activation in ASSD, autoantibody–mediated complement activation in IMNM, and a primary role of CD8⁺ T cells in IBM. This information is useful in developing unique therapeutic approaches to individual IIM subgroups. Although corticosteroids are still the first–line therapeutic agents, their long–term use is known to increase serious side effects that affect patients' quality of life and survival. Attempts to minimize the accumulated dosage and duration of corticosteroids has been made in patients with systemic lupus erythematosus, and are now applied to patients with IIMs. For this purpose, initial combination of immunosuppressive drugs and molecular–targeting drugs is being actively introduced in the field of IIMs. Over the next few years, management of IIMs will undergo major advances and will be able to provide better medical care to the patients.