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INTRODUCTION

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There are four major categories of idiopathic inflammatory myopathy: dermatomyositis (DM), polymyositis (PM), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM), which are clinically, histologically, and pathogenically distinct (Tables 33-1,33-2,33-3).112 These myositides may occur in isolation or in association with cancer, various connective tissue diseases (overlap syndromes), and autoantibodies. Other less common idiopathic myositides (i.e., granulomatous and myositis associated with infections) will also be discussed in this chapter. DM and IBM are rather homogeneous clinically and histologically. On the other hand, what has been called “PM” in the literature is likely a heterogeneous group of disorders. It is important to emphasize that not all myopathies with inflammation are classified as “inflammatory myopathies.” In this regard, various muscular dystrophies (e.g., congenital, facioscapulohumeral, and dysferlinopathies) may be associated with profound inflammation and are not uncommonly misdiagnosed as PM.

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Table Graphic Jump Location
TABLE 33-1.IDIOPATHIC INFLAMMATORY MYOPATHIES: CLINICAL AND LABORATORY FEATURES
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Table Graphic Jump Location
TABLE 33-2.DIAGNOSTIC CRITERIA FOR POLYMYOSITIS, DERMATOMYOSITIS, IMMUNE-MEDIATED NECROTIZING MYOPATHY, AND NONSPECIFIC/UNSPECIFIED MYOSITIS

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