Idiopathic inflammatory myopathies

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Abstract

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

Section snippets

Epidemiology

The IIM are rare sporadic disorders. The overall annual incidence of the IIM, using older diagnostic criteria, is approximately one in 100,000. Except for juvenile dermatomyositis, the IIM are diseases of the adult. They affect more women than men, except for IBM where the male-to-female ratio may be as high as 3/1. Interestingly, the age-adjusted prevalence of IBM in people over the age of 50 is 3.5/100,000, making it the most common IIM in this age group (Phillips et al., 2000). In the Mayo

Dermatomyositis

DM presents as an acute to insidious progressive, painless, proximal muscle weakness and/or a characteristic skin rash. Patients with acute disease and/or subcutaneous calcifications can have significant pain. Proximally predominant muscle weakness results in patients having difficulty using their arms while elevated over the head and being unable to get up from a deep chair or to climb stairs. This weakness pattern does not distinguish DM from many of the other myopathies. DM may result in

Inclusion body myositis

IBM is the most common myopathy after age 50. Symptom onset before age 60 occurs in 18% to 20% of patients (Lotz et al., 1989); (Badrising et al., 2005) with a frequent delay in diagnosis of five to eight years from IBM symptom onset (Lotz et al., 1989); (Badrising et al., 2000); (Lindberg et al., 1994); (Sayers et al., 1992). Men are more frequently affected than women with a ratio of 3/1.

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