Idiopathic Inflammatory Myopathies: Dermatomyositis And Polymyositis

Polymyositis is an inflammatory myopathy characterized by progressive, symmetric, proximal muscle weakness.  It is usually painless, although mild myalgia and muscle tenderness may occur.  Dermatomyositis is a similar disorder but is associated with certain typical skin findings.  Both conditions may occur independently or as a paraneoplastic manifestation of malignancy.

Recently, polymyositis as a distinct clinical entity has been questioned.  As diagnostic testing and classification schemes have been refined, many cases that were previously categorized as polymyositis can now be better classified as one of a group of immune-mediated myopathies (IMMs).  In addition to polymyositis and dermatomyositis, major IMM categories include inclusion body myositis, immune-mediated necrotizing myopathy, antisynthetase syndrome, and overlap myopathy (ie, myositis occurring in the context of another recognized autoimmune connective tissue disorder).