Complex repetitive discharge on electromyography as a risk factor for malignancy in idiopathic inflammatory myopathy.
OBJECTIVE
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.
Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
Na Ri
NR
Kim
Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
Eon Jeong
EJ
Nam
Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
Jong Wan
JW
Kang
Department of Neurology, Kyungpook National University School of Medicine, Daegu, Korea.
Hyun Seok
HS
Song
Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
Churl Hyun
CH
Im
Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
Young Mo
YM
Kang
D000200:Action Potentials; D000328:Adult; D000368:Aged; D003882:Dermatomyositis / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D004576:Electromyography; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D018482:Muscle, Skeletal / Q000294:innervation* / Q000473:pathology; D009369:Neoplasms / Q000209:etiology*; D016017:Odds Ratio; D017285:Polymyositis / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012307:Risk Factors
Dermatomyositis; Electromyography; Malignancy; Polymyositis; Risk factors