Epidemiology

Most studies reporting the incidence of idiopathic inflammatory myopathies (IIM) combine dermatomyositis (DM) and polymyositis (PM) and do not include patients with clinically amyopathic DM. In the US, the annual incidence of adult IIM is 5.5 to 8.9 cases per million.[5][6][7] There is a trend towards increasing incidence over time, but this is likely to reflect improved diagnosis and reporting rather than a true increase in disease incidence.[5][6][7] In Spain, the annual incidence of dermatomyositis has been determined at 4.9 per million.[8]

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