Idiopathic Inflammatory Myopathy Associated with Malignancy: A Retrospective Cohort of 151 Korean Patients with Dermatomyositis and Polymyositis

Abstract

To define the standardized incidence ratio (SIR) of malignancy and factors associated with malignancies in Korean patients with dermatomyositis (DM) and polymyositis (PM). The demographic, clinical, and laboratory features of 151 patients diagnosed with DM/PM were compared in patients with and without malignancies. Malignancies were found in 23 of 98 patients with DM (23.5%) and in 2 of 53 with PM (3.8%). Lung cancer (8 patients) was the most common malignancy. Compared with the period-specific, sex-matched, and age-matched Korean population, the SIR for malignancy in patients with DM was 14.2 (95% CI 9.0-21.3). Univariate analysis showed that factors associated with malignancy included older age (p < 0.001), DM (p = 0.002), dysphagia (p < 0.001), the absence of interstitial lung disease (ILD; p = 0.001), and lower elevations in aspartate aminotransferase (p = 0.005) and lactate dehydrogenase concentrations (p < 0.001). Multivariate analysis showed that factors independently associated with malignancy included older age (per 10 years, OR 2.3, 95% CI 1.6-3.5, p < 0.001), DM (OR 5.9, 95% CI 1.3-26.2, p = 0.020), dysphagia (OR 2.6, 95% CI 1.2-6.6, p = 0.042), and the absence of ILD (OR 0.1, 95% CI 0.01-0.9, p = 0.040). DM was associated with a greater risk of concomitant malignancies, especially lung cancer, than PM. Independent factors associated with malignancies in patients with DM/PM were older age, the presence of dysphagia, and the absence of ILD.