Epidemiologic analysis of the clinical features of Japanese patients with polymyositis and dermatomyositis

Objectives: This study aimed to investigate the clinical characteristics of polymyositis/dermatomyositis (PM/DM) in Japan by analyzing data from the nationwide registration system.Methods: The data of the registration system in 2009 were analyzed to investigate patient numbers, sex, clinical symptoms, therapies, complications, and prognosis of PM/DM.Results: The total number of PM/DM cases was approximately 17,000, and the female/male sex ratio was 2.7:1. Almost all patients improved as a result of therapy, but many suffered from sequelae such as muscle weakness.Conclusions: The results characterize significant aspects of Japanese PM/DM patients. However, a further prospective survey is required to clarify the true epidemiology and natural history of PM/DM.