Study of the Prevalence of Polymyositis and Dermatomyositis in Normandy

Polymyositis and dermatomyositis are characterized by the association to a myopathic syndrome, inflammatory infiltrates in the skeletal muscle. They remain, even today, an important factor of morbidity and mortality in these patients. At present, studies that evaluated the prevalence of polymyositis / dermatomyositis are very few; they were mainly recorded in the United States and Japan, the prevalence of polymyositis / dermatomyositis has been estimated between 3.5 and 21.5 cases / 100 000 (according to the old diagnostic criteria of Bohan and Peter). However, previous works are old and retrospective; above all, they have almost always been performed (90% of cases) from cases reported to the hospital, leading to selection bias and an underestimate of the true prevalence of polymyositis / dermatomyositis in the general population. Thus, these data lead to achieve this epidemiological study, descriptive, multicenter, based on the population of Normandy.