The objective of this study was to identify factors predictive of malignancy in patients with polymyositis (PM) and dermatomyositis (DM) in Japan. We conducted a retrospective study of PM and DM patients who were admitted to our hospital between January 1992 and September 2017. Among 134 patients, 29 (21.6%) were diagnosed with cancer in the 3 years prior to and 3 years after the initial diagnosis of PM or DM. According to multivariate analyses, male sex [odds ratio (OR) = 3.65, p = 0.03], old age (OR = 1.05, p = 0.02), and a past history of diabetes mellitus (OR = 10.4, p = 0.005) were associated with an increased risk of malignancy. The absence of interstitial lung disease (ILD) (OR = 0.25, p = 0.03) was also associated with an increased risk of malignancy. Diabetes mellitus was observed in 28.6% of PM and DM patients with malignancy, but in only 7.3% of those with malignancy. Survival was significantly lower in patients with malignancy than in those without malignancy (p < 0.001). Independent factors associated with malignancies in patients with PM or DM were male sex, old age, the absence of ILD, and, especially, a past history of diabetes mellitus.
Keywords: Dermatomyositis; Diabetes mellitus; Malignancy; Polymyositis.