Malignancy in dermatomyositis: A retrospective study of 201 patients seen at the University of Pennsylvania

Background There is an increased incidence of malignancy in patients with dermatomyositis. It is unknown if the risk differs between the subtypes of dermatomyositis. Objective To (1) compare the prevalence of malignancy-associated dermatomyositis between patients with classic and clinically amyopathic disease and (2) determine factors associated with an increased risk of malignancy-associated disease. Methods Retrospective cohort study of 201 patients with adult-onset dermatomyositis prospectively enrolled in a longitudinal dermatomyositis database between July 2008 and April 2018 at an outpatient dermatology urban tertiary referral center. The main outcome measure was a diagnosis of malignancy, excluding nonmelanoma skin cancer. Results There were 201 patients with adult-onset dermatomyositis: 142 (71%) classic and 59 (29%) clinically amyopathic. Within 2 years of diagnosis, the prevalences of malignancy-associated classic and clinically amyopathic dermatomyositis were 9.9% and 1.7%, respectively. In this time period, patients who were older at dermatomyositis diagnosis (P = .01) and had the classic subtype (P = .04) were significantly more likely to have an underlying malignancy on multivariable regression analysis. Limitations This was a retrospective study of prospectively collected data at a single tertiary referral center. Conclusion Older age and classic dermatomyositis are independent risk factors for malignancy-associated dermatomyositis within 2 years of disease onset.