ABSTRACT
Polymyositis (PM) and dennatomyositis (OMS) are disorders of muscle inflammation with unknown etiology (1-6). These disorders belong to the group of inflammatory myopathies that also includes the less common entity of inclusion-body myositis. These disorders are rare. The incidence of PM/DMS has been reported to be 0.2-0.55 new cases per 100,000, or roughly 10 new cases per million persons per year (7 ,8). Recent data from a collaborative pediatric rheumatology database in northeastern United States show the mean annual incidence of juvenile DMS to be 0.4 new cases per 100,000 children (9). PM is more commonly seen in adults and rarely in childhood, whereas DMS is seen in children and adults.
