Recognition and management of myositis.

Polymyositis and dermatomyositis are severe inflammatory muscle disorders of unknown cause, with possible life-threatening complications. Prognosis and response to therapy may be predicted not only from the clinical and pathological diagnostic group to which a patient belongs, but also from the patient's myositis-specific antibody status, extraskeletal muscle involvement, and the interval between onset of muscle weakness and the start of the treatment. Corticosteroids are the mainstay of treatment, providing recovery of normal muscular function in about 60% of patients. However, adequate dose, duration of therapy and gradual tapering of corticosteroids are required to produce favourable biochemical and clinical outcomes. In patients refractory to or intolerant of corticosteroids, additional therapy, often involving an immunosuppressive agent or intravenous immunoglobulin, is required. The potential roles of plasmapheresis and total body irradiation must be balanced by their inconclusive efficacies and adverse effects.