Polymyositis and dermatomyositis in children: an epidemiologic and clinical comparative analysis.

In an attempt to delineate and compare the clinical, laboratory and epidemiologic features of polymyositis (PM) and dermatomyositis (DM) in children, the records of all 19 hospitals in Memphis and Shelby County, Tennessee, were surveyed over the 25-year period, 1948-1972. Seventeen documented cases of PM and 26 of DM were identified over the total period. PM was not diagnosed prior to 1962, while DM was found throughout the study. A significant female excess was observed in the PM group and in the combined patients 10-19 years of age. The only major differences found between PM and DM were the more acute and severe muscle involvement in DM and its cutaneous manifestations. Juvenile PM is a definite entity which should be differentiated from other myopathies because of its favourable response to corticosteroid therapy.