Abstract

The inflammatory myopathies, including dermatomyositis, inclusion body myositis, and polymyositis, are poorly understood autoimmune diseases affecting skeletal muscle. Dermatomyositis is a disease mainly of skin and muscle, but may affect lung and other tissues. Proximal or generalized weakness or skin rash are the typical presenting features. Inclusion body myositis has a specific clinical pattern of weakness that generally distinguishes it from other inflammatory myopathies, with prominent involvement of wrist and finger flexors, and quadriceps. Polymyositis generally presents with proximal or generalized weakness. Typical dermatomyositis muscle pathology is quite distinct, with perivascular inflammatory cells that include plasmacytoid dendritic cells, and abnormal capillaries and perimysial perifascicular myofibers. Both inclusion body myositis and polymyositis usually have infiltration into muscle of large numbers of inflammatory cells, typically surrounding and displacing, and sometimes invading, myofibers. Inclusion body myositis is refractory to corticosteroids and to several immunomodulating therapies that have been used. Dermatomyositis and polymyositis are treated with corticosteroids and a variety of agents. Osteoporosis and opportunistic infections pose a significant risk during treatment of patients. This review discusses the clinical manifestations, pathology, and treatment approaches for the inflammatory myopathies.