Background: Adult onset idiopathic inflammatory myopathies are serious disorders with potential to cause serious morbidity and mortality.
Objectives: To evaluate the survival data for patients with idiopathic inflammatory myopathies by determining the cumulative survival probability, long term prognosis and analyzing the causes of death.
Methods: Adult patients (>18 years) with idiopathic inflammatory myopathies (polymyositis and dermatomyositis), diagnosed between 1989 to May 2006, fulfilling the Bohan and Peter’s criteria were enrolled in the study. Clinical and demographic profile was noted from the record files. Kaplan-Meyer analysis was used to estimate survival. Univariate and multivariate Cox regression analysis were used to study clinical associations with mortality.
Results: There were 95 patients (F:M ratio 2.8:1), mean age 34.3 years  11.1 (range 18-68), and median disease duration of 7 months (range 1-168). There were 63 patients in dermatomyositis group (DM) and 32 in the polymyositis group (PM). Patients were followed up for a median of 39 months in the DM and 57 months in the PM group. There were eight deaths in the DM as compared to two in the PM group (p<0.005). The cumulative survival probability by Kaplan-Meier method was 92%, 90%, and 79% at 1, 2, and 7 years for the DM group whereas it was 96% and 93% at 1 and 7 years for the PM group. Advanced age (p=0.012) and presence of respiratory (p=0.042), and pharyngeal (p=0.036) muscle weakness were significant prognostic factors for death. Ten patients in the DM and six in the PM groups had relapses during the course of follow-up. At last visit, however, only 21% (14.2% in DM and 34.3% in PM group) of the patients were in complete remission without the need of immunosuppressive therapy. Of ten deaths, four each were due to aspiration pneumonia and infections, and one each died due to gastrointestinal perforation and disseminated malignancy.

Conclusion: Adult onset dermatomyositis presenting with respiratory or pharyngeal muscle weakness portends poor prognosis. Most patients continued to need long term immunosuppressive therapy.