Background/Purpose: Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of autoimmune diseases, with low prevalence and 5-year survival of 70-95%. Previous studies in Mexican IIM patients suggest differences compared to other ethnic groups in clinical presentation, response to treatment, prognosis and autoantibodies. The aim of this study was to estimate the survivor function of IIM Mexican patients and identify factors associated to mortality.

Methods: This is a retrospective cohort study including patients with Dermatomyositis (DM) and Polymyositis (PM) according to Bohan and Peter’s criteria, seen at a tertiary care center from January 1985 to January 2012. Baseline demographic, clinical variables, comorbidities, systemic manifestations and muscular strength were registered. The time to death, last medical evaluation or loss of follow up was obtained. Censoring time was established as the last medical visit. Univariate and multivariate Cox regression analysis were done to analyze factors associated with mortality. All analysis were two tailed, alpha was set at 5%.

Results: 304 DM and 71 PM patients were included, 70% female. At baseline evaluation, patients with DM were younger (p<0.005) and PM patients had higher CPK levels (p<0.004). DM patients had lower survivor function than those with PM during the first 4 years of follow up (log Rank test, p<0.041, Fig. 1). Respiratory failure secondary to pneumonia was the principal cause of death in DM patients (26/56, (46%)). Miscellaneous causes were responsible of death in PM patients. In univariate analysis, the variables associated with mortality during the first 4 years of disease in DM patients were: Age at onset (HR 1.03, 95% CI 1.01-1.05, p<0.001), cancer (HR 2.58, 95% CI 1.33–5.04, p<0.02), muscular strength (HR 0.60, 95% CI 0.45-0.80, p< 0.002), hemoglobin (HR 0.78, 95% CI 0.68-0.89, p<0.0001), serum albumin (HR 0.33, 95% CI 0.23–0.42, p<0.001), creatinine (HR 1.88, 95% CI 1.08-3.27, p<0.03), platelet count (HR 0.99, 95% CI 0.990-0.999, p<0.04), ever use of methotrexate and azathioprine (RM 0.19, 95% CI 0.09-0.40, p<0.0001). In the multivariate analysis, age at onset (HR 1.03, 95% CI 1.01-1.06, p<0.002), cancer (HR 2.55, 95% CI 1.1-6.4, p<0.05) and muscular strength (HR 0.54, 95% CI 0.34-0.84, p<0.006) were independent factors associated with mortality. In patients with PM, the only variable associated with mortality was cancer (HR 8.22, 95% CI 1.5-44.98, p<0.02).

Conclusion: Patients with DM had lower survival rate during the first 4 years of disease than patients with PM. Respiratory failure secondary to pneumonia was the main cause of death in DM patients. Factors associated to mortality differed in DM and PM. In DM patients, age of disease onset, cancer, and level of muscle strength were associated with mortality; in PM patients only cancer was associated.