Long-term follow-up of 124 patients with polymyositis and dermatomyositis: Statistical analysis of prognostic factors

Objectives. The aims of this study were to clarify the long-term outcome of patients with polymyositis and dermatomyositis (PM/DM) and to elucidate prognostic factors using statistical analysis.Methods. We enrolled patients with PM/DM who visited our department between 1990 and 2014. Diagnoses of PM/DM and clinically amyopathic DM were based on the definitions of Bohan and Peter, and Sontheimer, respectively. We also obtained clinical data, such as age of onset, sex, medications, and presence of interstitial lung disease and malignancies, as well as laboratory tests, including the values of creatine kinase, KL-6, and ferritin. The follow-up was conducted until June 2014.Results. A total of 124 patients (PM: 46, DM: 78) were enrolled. The mean age of onset was 53.5 years, and females were predominant (64.5%). Overall survival rates were 93%, 86%, and 78% for 1, 5, and 10 years, respectively. The survival rates were significantly lower in patients with higher age of onset, with malignancies, and with hyperferritinemia in univariate analysis; however, multivariate analysis identified age of onset and serum ferritin as the most significant prognostic factors.Conclusions. Our study indicates that when age of onset and serum ferritin are used in combination, we can predict prognosis of patients with PM/DM.