Long-term survival of patients with idiopathic inflammatory myopathies according to clinical features: a longitudinal study of 162 cases

Abstract

The idiopathic inflammatory myopathies are characterized by chronic muscle inflammation and involvement of internal organs, which contribute considerably to the morbidity and mortality of the disease. We conducted the current study to determine the survival data for patients with idiopathic inflammatory myopathies according to the presence of extramuscular clinical manifestations. We also determined the cumulative survival probability and the long-term prognosis and analyzed the causes of death at a single clinical immunology center.A survival analysis was performed using data for 162 patients diagnosed between 1976 and 1997 according to Bohan and Peter's criteria. Patients were followed up for a minimum of 5 years (median, 101.5 mo) or to date of death. Cumulative survival probability was calculated by the Kaplan-Meier method. The influence of extraskeletal and extramuscular involvement was analyzed as prognostic factors for death by Cox proportional hazards survival model. Eighteen disease-specific deaths occurred; pulmonary and cardiac complications were the most frequent causes of death. Global survival rates were 95%, 92%, and 89% for 1, 5, and 10 years, respectively. Analysis for clinicopathologic subgroups revealed that cancer-associated myositis had the worst prognosis, while juvenile and overlap myositis had the best prognosis. Five- and 10-year survival rates were 94.2% and 89.4% for patients with primary polymyositis and 90.1% and 86.4% for primary dermatomyositis patients, respectively. In the whole group of patients with idiopathic inflammatory myopathy, cardiac (p < 0.01) and respiratory muscle involvement (p = 0.045) were significant prognostic factors for death. In the group of patients with primary polymyositis/dermatomyositis, cardiac involvement was the main prognostic factor for death (p < 0.01). Myositis patients described in this study have higher survival rates than reported previously worldwide. We examine the reasons for the differences between the data in the current study and the available survival data in the relevant literature.