Objectives: Several factors have been implicated in the prognosis of idiopathic inflammatory myopathies, including age, gender, delay in diagnosis, neoplasia, creatine kinase levels and some autoantibodies. We have reviewed the main factors contributing to mortality in patients with idiopathic inflammatory myopathy (IIM) diagnosed between 1976 and 2007 who were followed for at least 5 years in the Rheumatology Unit at University College Hospital in London.
Methods: An observational retrospective study was carried out on patients with IIM diagnosed between 1976 and 2007. All the patients fullfilled at least three out of four of the Bohan and Peter criteria. The subjects were divided into the following groups: adult-onset polymyositis (APM); adult-onset dermatomyositis (ADM); juvenile dermatomyositis (JDM); Overlap syndromes with another autoimmune rheumatic disease.
Results: 90 patients were identified. The female to male ratio was 2.5:1 and the mean age at diagnosis was 38.5 years (SD 15.03). 47.8% of the patients had APM, 30% adult-onset ADM, 15.6% Overlap and 6.7% JDM. Among the extramuscular features, 18.9% had pulmonary involvement. In 70% the highest CK was >5 times the upper normal. Prednisolone was prescribed in 98.9%. 11.1% received rituximab. 34.4% had monophasic, 31.1% relapsing and remitting and 34.4% continuous progressive course of the disease. The median follow-up was 11.5 years (IQR 12.00). 14.4% of the patients died, 30.8% due to infection, 30.8% from a cardiovascular event and 23.1% due to neoplasia. The 1, 5 and 10-year survival was 100%, 97.8% and 91%, respectively. Male gender (Hazards Ratio (HR) 3.222; p=0.037), pulmonary involvement (HR 5.247; p=0.009), chronic progressive course (HR 3.711; p=0.030) and use of rituximab (HR 3.562; p=0.036) were the only risk factors to be statistically significantly associated (p<0.05) with death.
Conclusions: We conclude that long-term survival in these patients is generally quite good with an estimated 10-year survival >90% in our cohort, which is even higher than previously reported.