Mortality from polymyositis and dermatomyositis in the United States, 1968-1978.

Mortality from polymyositis and dermatomyositis was estimated between 1968 and 1978. Age-specific average annual mortality rates showed unimodal distributions for all sex-race groups. Synergistic interaction was demonstrated between female sex and nonwhite race, greatest mortality being in nonwhite females through age 74. Increases in annual death rates occurred among both white males and white females during the interval. Finally, the increase in mean age at death among all sex groups correlated with improved prognosis as well as decreased mortality among younger persons over time.