Is there an association between injectable collagen and polymyositis/dermatomyositis?

OBJECTIVE Recent case reports have raised the possibility that use of injectable bovine collagen may be associated with polymyositis/dermatomyositis (PM/DM). Because the number of collagen users is high, PM/DM would be expected to occur in some for reasons unrelated to the collagen use. A central issue is whether the number of observed cases exceeds the number expected on the basis of background rates alone. The present study was undertaken to investigate this. METHODS The number of observed cases was determined by review of the medical records of collagen users who had reported illnesses consistent with PM/DM: Because of the uncertainty about diagnosis of PM/DM, population incidence rates, number of patients treated with collagen, and duration of followup after treatment, we examined a range of estimates of each of these factors that would affect the expected number of cases. RESULTS From reports among collagen users, 7 probable or definite cases of PM/DM were confirmed. In contrast, 13 cases would be expected based on the best estimates of relevant factors. Under the most conservative estimates for factors that influence the number of expected cases, 12 cases would be expected, while worst-case assumptions would yield an expected 130 cases. CONCLUSION The consistent finding of fewer-than-expected PM/DM cases among collagen users suggests that collagen use is not associated with the development of PM/DM: