Complex repetitive discharge on electromyography as a risk factor for malignancy in idiopathic inflammatory myopathy

Background/Aims: We investigated the electromyography (EMG) findings and demographic, clinical, and laboratory features that may predict the development of malignancy in patients with idiopathic inflammatory myopathy (IIM). Methods: In total, 61 patients, 36 with dermatomyositis and 25 with polymyositis, were included. Patients were divided into those with and without malignancies, and comparisons were made between the groups in terms of their demographic, clinical, laboratory, and EMG findings. Results: The frequencies of malignancies associated with dermatomyositis and polymyositis were 22% and 8%, respectively. Patients with malignancies showed a significantly higher incidence of dysphagia (odds ratio [OR], 21.50; 95% confidence interval [CI], 3.84 to 120.49), absence of interstitial lung disease (ILD; OR, 0.12; 95% CI, 0.01 to 0.98), and complex repetitive discharge (CRD) on the EMG (OR, 26.25; 95% CI, 2.67 to 258.52), versus those without. After adjustment for age, dysphagia and CRD remained significant, while ILD showed a trend for a difference but was not statistically significant. Multivariate analysis revealed that the CRD conferred an OR of 25.99 (95% CI, 1.27 to 531.86) for malignancy. When the frequency of malignancy was analyzed according to the number of risk factors, patients with three risk factors showed a significantly higher incidence of malignancy, versus those with fewer than two (p = 0.014). Conclusions: We demonstrated for the first time that CRD on the EMG was an additional independent risk factor for malignancy in IIM. Further studies on a larger scale are needed to confirm the importance of CRD as a risk factor for malignancy in IIM.