Investigation on Serum Levels of Interleukin-18 and Interleukin-6 in Patients With Dermatomyositis and Polymyositis

Dermatomyositis (DM) and polymyositis (PM) are common forms of idiopathic inflammatory myopathy which are characterized by muscle inflammation with an unknown cause. Immune cells infiltrate myofibrils and endomysial capillaries, which leads to damage of muscle fibers through the production of humoral factors and different cytokines. Increased IL-18 and IL-6 serum levels have been reported in a variety of autoimmune diseases, including rheumatoid arthritis and inflammatory bowel disease. The purpose of this study was to evaluate IL-18 and IL-6 serum levels in DM and PM patients compared to a healthy control group. In this cross-sectional study, 15 patients with DM, 5 patients with PM, and 20 healthy control subjects were recruited. The levels of serum IL-18 and IL-6 in patients and control groups were measured by using ELISA assay. Blood tests were taken to determine the levels of C-reactive protein (CRP) and creatine kinase (CK) and were measured by standard methods. Statistical analyses were performed using the Mann-Whitney U-test with a non-Gaussian population using SPSS 19 software. IL-18 levels were significantly higher in DM patients and PM patients before treatment compared to healthy control subjects (P = 0.001, P = 0.01, respectively). There were no significant differences between DM and PM patients before treatment with healthy controls for IL-6 serum levels (P = 0.51, P = 0.43, respectively). Serum IL-18 contributes to the immunopathogenesis of DM and PM and would be a useful marker for the diagnosis and treatment of diseases. IL-6 has a less pivotal role in the pathology of DM and PM.