Risk assessment of polymyositis dermatomyositis after treatment with injectable bovine collagen implants

Background: Questions have been raised about a possible relation between injectable collagen and polymyositis and dermatomyositis (PM/DM). Predictions of the prevalence of PM/DM have been based on anecdotal estimates of the duration of fellow-up for the collagen-treated population. Objective: Our purpose was to study the duration of follow-up for a large sample of collagen-treated patients. Methods: Physicians in North America who purchased collagen implants during fiscal year 1988 were categorized according to collagen practice size; one third were randomly invited to participate in the study. Results: Review of 2622 patient records yielded an average duration of follow-up of 4 years. Conclusion: Five-year incidence rates were used to estimate the expected number of cases of PM/DM in the collagen-treated population. Through June 1993 the expected number was 30.2, The number of confirmed cases after treatment was seven, less than one fourth of the number of cases expected for a model of the collagen-heated population, matched for age, sex, and race.