Impact of treatment on survival in polymyositis and dermatomyositis. A single-centre long-term follow-up study.

OBJECTIVE: To assess the long-term outcome in polymyositis (PM) and dermatomyositis (DM), with a particular emphasis on mortality and influence of treatment. METHODS: Diagnosis was based according to the Bohan and Peter's criteria. Patients have been followed up by a standardised protocol. Deaths were registered and causes of death were ascertained. Survival probability at 5 and 10years was estimated according to the Kaplan-Meier method, in the overall series and by a diagnostic group and an initial treatment. Mortality hazard ratios (95% CI) for major clinical and demographic features were estimated through univariate and multivariate Cox proportional hazard models. RESULTS: 91 patients (43 PM and 48 DM) were available for the study. Baseline characteristics were not different from those previously reported. Twenty-two patients (24%) died after a median follow-up of 8.7years. As for idiopathic myositis, the survival probabilities at 5 and 10years from the diagnosis were 96.2% and 88.8% for PM respectively; and 93.9% for DM, whereas a higher mortality was documented for cancer-associated myositis and overlap myositis. Male sex [HR=2.4, 95% CI 1.0 to 5.6], heart involvement (HR=1.8), interstitial lung disease (HR=2.3) and arthritis (HR=1.8) increased the risk of mortality, these risk excesses were confirmed in the multivariate analysis. Independent of these features, a higher mortality was documented for patients treated with glucocorticoids (HR=2.3) or immunosuppressants (HR=2.1) when compared to patients treated with immunoglobulins. CONCLUSION: Our study, with longitudinal and statistical analyses, suggests that survival has considerably increased in patients with PM/DM. Prognostic factors for mortality are male sex, and heart and lung involvement. Immunoglobulin treatment, intravenously or subcutaneously, is associated with a better survival.