Polymyositis and dermatomyositis: Disease spectrum and classification

Muscle inflammation and weakness are the key features of idiopathic inflammatory myopathies (IIMs). In addition IIMs are frequently associated with cutaneous and pulmonary involvement. In clinical practice the three common inflammatory myopathies we come across are polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM). The Bohan and Peter criteria combine clinical, laboratory, and pathologic features to define PM and DM. They did not recognize inclusion body myositis (IBM) or other inflammatory myopathies, such as granulomatous and eosinophilic myositis. Thus the disease spectrum is wide and IIMs are a heterogeneous group of autoimmune disorders. To address these issues in this article we have discussed the currently developing newer classifications of IIMs.