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.