Idiopathic inflammatory myopathies.

The idiopathic inflammatory myopathies (IIM) encompass a heterogeneous group of rare disorders that present with acute, subacute, or chronic muscle weakness. Besides overlapping clinical manifestations, polymyositis, dermatomyositis and autoimmune necrotizing myopathy may be associated with cancer or collagen vascular disease, and respond generally well to immunosuppressive therapy. However, these 3 IIM are divergent from the histopathological and pathogenetic standpoints. On the other hand, inclusion body myositis (IBM), the most common IIM in the elderly, is clinically, histopathologically and pathogenetically distinct. IBM is also refractory to all currently available therapies. In this manuscript, we depict advances in our knowledge of the IIM, with emphasis on clinical presentation, associated conditions, laboratory features, electrophysiology, muscle histopathology, pathogenesis, and therapy.