Retrospective evaluation of malignancies accompanying inflammatory muscle diseases

Objective: Inflammatory muscle diseases (IMD) are autoimmune myopathies characterized by progressive proximal muscle weakness and distinctive skin findings. Polymyositis (PM) and dermatomyositis (DM) are the two most common subtypes of IMD. IMDs are systemic diseases that can affect organs such as skin, joints, lungs, esophagus, and heart, in addition to muscle involvement. One of the most significant common features of these diseases is their association with malignancies. The aim of our study was to determine the clinical and laboratory characteristics of patients diagnosed with IMD, identify factors influencing prognosis, compare our results with other data in the literature, and determine the response rates to treatment in our patients. Materials and Methods: A total of 87 patients diagnosed and treated with inflammatory muscle diseases (IMD) according to the 1975 Bohan-Peter diagnostic criteria in the Rheumatology Department were retrospectively evaluated. Clinical, laboratory, radiological, and histopathological parameters were examined. Statistical analysis of the data was performed using SPSS (Statistical Package for the Social Sciences) version 25.0. Results: 87 patients diagnosed with inflammatory muscle diseases were included in the study. The average age of the patients was 51.3±14.5 years. 69 (79.3%) of the patients were female and 18 (20.7%) were male. When the distribution of myositis subgroups is examined; 48 patients (55.17%) had Polymyositis (PM) and 39 patients (44.83%) had Dermatomyositis (DM). Malignancy was detected in 15 (17.2%) of the patients. Among the patients detected with malignancy, the most common ones were breast cancer in 4 (20.1%), ALL (Acute lymphoblastic leukemia) in 2 (13.3%), ovarian cancer in 2 (13.3%), and ovarian cancer in 2 (13.3%). Papillary thyroid cancer was detected in 13.3 patients. Lung Adenocarcinoma, Small cell lung cancer (SCLC), CLL (Chronic lymphoblastic leukemia), Colon adenocarcinoma, Non-Hodgkin lymphoma (NHL), and Undifferentiated Nasopharynx cancer were detected in one patient each. Conclusion: In conclusion, we found an overall increase in the incidence of malignant disease in both men and women in inflammatory muscle diseases. The overall risk is highest in the first 2.6-4.4 years after myositis is diagnosed. An increased incidence of concurrent and sequential malignant disease was detected in both PM and DM, but the relative risk was higher in dermatomyositis, adjusted for age, sex, and time since myositis diagnosis. Keywords: Inflammatory muscle diseases, Dermatomyositis, Polymyositis, Rose-Walton score, Malignancy.