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Fifty years ago, the prognosis for these conditions was poor, with high morbidity and mortality, and very few treatments were available. Since then, there has been major growth in our understanding of the pathogenesis and evidence basis for treatment. Early descriptions considered juvenile dermatomyositis (JDM) to be essentially one disease. Our modern understanding has shown that there are different types of JIIMs, and that although JDM remains the most prevalent, even JDM itself is highly heterogenous. Much progress has been made possible through concomitant growth in the research community with a focus on JIIMs and the fact that the myositis research and clinical communities are highly collaborative internationally. Here, we review the growing understanding of the different types of childhood myositis; the developments in classification, driven in part by recognition of associations of particular phenotypes with specific myositis autoantibodies; the novel insights into pathogenesis of the JIIMs; the therapeutic targets that these have revealed; and the evidence for, and development of, modern treatment care pathways, which have changed radically in recent decades. This has resulted in improved outcomes for children and young people with JIIMs and hope for further groundbreaking developments.<\/jats:p>","DOI":"10.1002\/acr.80115","type":"journal-article","created":{"date-parts":[[2026,7,13]],"date-time":"2026-07-13T11:46:42Z","timestamp":1783943202000},"page":"1346-1357","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Juvenile Myositis: Insights on Classification, Pathogenesis, and Therapies Over the Past 50 Years"],"prefix":"10.1002","volume":"78","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7495-1429","authenticated-orcid":false,"given":"Lucy R.","family":"Wedderburn","sequence":"first","affiliation":[{"name":"Infection, Immunity and Inflammation Research and Teaching Department University College London Great Ormond Street Institute of Child Health  London United Kingdom"},{"name":"Centre for Adolescent Rheumatology at University College London University College London Hospitals and Great Ormond Street Hospital  London United Kingdom"},{"name":"NIHR Biomedical Research Centre at Great Ormond Street Hospital NHS Foundation Trust  London United Kingdom"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7813-9665","authenticated-orcid":false,"given":"Brian M.","family":"Feldman","sequence":"additional","affiliation":[{"name":"Division of Rheumatology, Department of Pediatrics The Hospital for Sick Children  Toronto Ontario Canada"},{"name":"Institute of Health Policy Evaluation &amp; Management University of Toronto  Toronto Ontario Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6912-2458","authenticated-orcid":false,"given":"Lisa G.","family":"Rider","sequence":"additional","affiliation":[{"name":"Environmental Autoimmunity Group, Clinical Research Branch, National Institute of Environmental Health Sciences, National Institutes of Health  Bethesda Maryland"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2026,9,9]]},"reference":[{"key":"e_1_2_4_2_1","doi-asserted-by":"publisher","DOI":"10.1097\/BOR.0000000000000119"},{"issue":"2","key":"e_1_2_4_3_1","first-page":"178","article-title":"Shared governance of international myositis networks","volume":"44","author":"Liewluck T","year":"2026","journal-title":"Clin Exp Rheumatol"},{"key":"e_1_2_4_4_1","doi-asserted-by":"publisher","DOI":"10.1002\/acr.20532"},{"key":"e_1_2_4_5_1","doi-asserted-by":"publisher","DOI":"10.1002\/art.40060"},{"key":"e_1_2_4_6_1","doi-asserted-by":"publisher","DOI":"10.1002\/art.37754"},{"key":"e_1_2_4_7_1","doi-asserted-by":"publisher","DOI":"10.1002\/art.40320"},{"key":"e_1_2_4_8_1","doi-asserted-by":"publisher","DOI":"10.1136\/annrheumdis-2016-209247"},{"key":"e_1_2_4_9_1","doi-asserted-by":"publisher","DOI":"10.1186\/s12969-016-0134-0"},{"key":"e_1_2_4_10_1","doi-asserted-by":"publisher","DOI":"10.1002\/acr.20071"},{"key":"e_1_2_4_11_1","doi-asserted-by":"publisher","DOI":"10.55563\/clinexprheumatol\/zka1xq"},{"key":"e_1_2_4_12_1","volume-title":"Myositis and You: A Guide to Juvenile Dermatomyositis for Patients, Families, and Healthcare Providers","author":"Rider LG","year":"2007"},{"key":"e_1_2_4_13_1","doi-asserted-by":"publisher","DOI":"10.1056\/NEJM197502132920706"},{"key":"e_1_2_4_14_1","doi-asserted-by":"publisher","DOI":"10.1097\/00005792-199111000-00002"},{"key":"e_1_2_4_15_1","doi-asserted-by":"publisher","DOI":"10.1002\/art.1780371019"},{"key":"e_1_2_4_16_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0889-857X(05)70350-1"},{"key":"e_1_2_4_17_1","doi-asserted-by":"publisher","DOI":"10.1111\/joim.12444"},{"key":"e_1_2_4_18_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.jaut.2017.06.007"},{"key":"e_1_2_4_19_1","doi-asserted-by":"publisher","DOI":"10.1002\/art.42813"},{"key":"e_1_2_4_20_1","doi-asserted-by":"publisher","DOI":"10.1002\/acr.23113"},{"key":"e_1_2_4_21_1","doi-asserted-by":"publisher","DOI":"10.1111\/joim.12451"},{"key":"e_1_2_4_22_1","first-page":"533","article-title":"Acute progressive polymyositis. 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