Newer Therapeutic Approaches: Inflammatory Muscle Disorders

The idiopathic inflammatory myopathies are a group of systemic diseases characterized by an immune-mediated attack on skeletal muscle that results in weakness. In adults, inflammatory myopathy includes the diagnostic entities of polymyositis, dermatomyositis, and inclusion-body myositis. Inflammatory myopathy may also be classified in terms of the clinical syndromes that are associated with one of several myositis-specific autoantibodies (MSAs), such as the antisynthetase and anti–signal recognition peptide syndromes, that may be associated with any of the three forms of myopathy. The members of this group differ in clinical presentation, histopathology, and response to treatment, suggesting different disease pathogenic pathways; however, the treatment strategy for each is similar, if not identical. As with other systemic connective tissue inflammatory diseases, the cause of these disorders remains unknown, but well-recognized clinical associations may provide clues about possible etiological factors. The inflammatory myopathies, dermatomyositis in particular, have been associated with the presence of malignancy; furthermore, myopathy may improve with removal or treatment of the cancer. These factors suggest a possible link between mechanisms leading to or allowing the development of neoplasia and chronic muscle-targeted inflammation. In addition, the inflammatory myopathies may be associated with the presence of other autoimmune diseases, such as systemic lupus erythematosus