Myositis

Abstract

Myositis (inflammation of skeletal muscles) has many causes (Figure 1). Many viruses and drugs can induce transient disease. In contrast, bacterial infection causes pyomyositis with acute focal suppuration and abscess formation. This contribution focuses on idiopathic inflammatory myositis characterized by chronic inflammation of striated muscle (polymyositis) sometimes with involvement of the skin (dermatomyositis). Focal nodular myositis, giant cell myositis and eosinophilic myositis are rare conditions with characteristic features on muscle biopsy; they are not covered in detail here. Idiopathic inflammatory myositis is classified as: •primary idiopathic polymyositis •primary idiopathic dermatomyositis •dermatomyositis/polymyositis associated with neoplasia •childhood dermatomyositis/polymyositis associated with vasculitis •polymyositis/dermatomyositis associated with autoimmune disease •inclusion body myositis.