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.