[Inflammatory muscle diseases: dermatomyositis, polymyositis, and inclusion body myositis]

Dermatomyositis, polymyositis, inclusion body myositis and myositis overlap syndromes are systemic immune disorders of unknown origin with muscle weakness and elevated values of creatinkinase in the serum. Muscle biopsy is pivotal for a proper clinical diagnosis. Extramuscular findings at the skin, the joints or internal organs (lung, heart) are characteristic for the different clinical presentations of dermato- or polymyositis and are usually absent in inclusion body myositis. With the exception of inclusion body myositis myositis-associated autoantibodies are frequently present and associated with distinct clinical manifestations (e. g. antisynthetase syndrome). The rate of malignancy is elevated for several years after onset of myositis. Especially in polymyositis an appropriate differential diagnosis of infectious, endocrine, metabolic or neuromuscular causes of muscle disease is necessary. Glucocorticosteroids are the first choice of treatment in dermato- or polymyositis. Methotraxate, azathioprine, cyclophosphamamide, i.v. immunoglobulins and other drugs are used in diseases courses with continuous high dose requirement of corticosteroids.