Epidemiology of the idiopathic inflammatory myopathies

Thomas Khoo, James Lilleker, Bernard Yu-Hor Thong, Valérie Leclair, Janine Lamb, Hector Chinoy

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The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of systemic autoimmune diseases that affect the skeletal muscles and can also involve the skin, joints, lungs and heart. The epidemiology of IIM is obscured by changing classification criteria and the inherent shortcomings of case identification using health-care record diagnostic coding. The incidence of IIM is estimated to range from 0.2 to 2 per 100,000 person-years, with prevalence from 2 to 25 per 100,000 people. Although the effects of age and gender on incidence are known, there is only sparse understanding of ethnic differences, particularly in indigenous populations. The incidence of IIM has reportedly increased in the 21st century, but whether this increase is genuine is not yet known. Our understanding of the genetic risk factors for different IIM subtypes has advanced considerably. Infections, medications, malignancy and geography are also commonly identified risk factors. Potentially, the COVID-19 pandemic has altered IIM incidence, although evidence for this occurrence is limited to case reports and small case series. A consideration of our current understanding of the epidemiology of, and risk factors for, IIM can highlight the important areas of interest for future research into these rare diseases.

Original languageEnglish
JournalNature Reviews. Rheumatology
Publication statusAccepted/In press - 5 Sept 2023


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