Predisposing factors in polymyositis-dermatomyositis: results of a nationwide survey.

Utilizing case-control methods, we surveyed 322 persons who experienced the onset of polymyositis-dermatomyositis (PM-DM) during calendar years 1985 and 1986, in an effort both to test specific hypotheses, and to generate new hypotheses regarding antecedent risk associations for the disease. Data obtained by recall of events during the 12 months before disease onset in cases, and an identical time period in sex matched sibling controls, suggest that important questions for further study include the roles of antecedent heavy muscular exertion and emotional stress as risk factors for PM-DM. Furthermore, it appears that vaccinations, toxic exposures and symptoms of allergic phenomena, throat infection, and upper respiratory infection are either neutral or are negatively associated with risk of PM-DM, findings which also raise important new etiologic questions, or perhaps lay old ones to rest. Malignancy was infrequently noted.