update on inflammatory myopathies

Inflammatory myopathies are heterogeneous groups of immune mediated myopathies that present as pure form or in association with other auto-immune diseases or malignancy. There are three major subsets: dermatomyositis, polymyositis and sporadic inclusion body myositis. This review highlights our understanding of these disorders, their clinical aspects, diagnosis, pathogenesis and treatment. The idiopathic inflammatory myopathies occurring alone or in association with auto-immune disease and / or cancer have an overlapping clinical presentation with an overall incidence of 3.0 to 7.8 per million and a prevalence from 10 to 60 per million. Because of the variability in epidemiological studies, the interpretation of these results cannot be conclusive. Recent evidence indicates that polymyositis is over diagnosed and many reported cases are likely to be some other disorders. Decreasing the incidence of true polymyositis is due to reliance not only on clinical criteria but also on immunopathological changes in muscle biopsies. Polymyositis and inclusion body myositis occur primarily in adults, whereas dermatomyositis occurs in adults and children between five and fifteen years of age. Sporadic inclusion body myositis affects almost exclusively men over the age of 50 years