The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of disorders characterized by varied patterns of inflammation within striated muscle. The major disease categories among the IIM are der-matomyositis (DM), polymyositis (PM), inclusion body myositis (IBM), myositis associated with connective tissue diseases, and myositis associated with malignancy. The skin, joints, lungs, heart, and gastrointestinal tract are also involved in different forms of these disorders. Muscle weakness that is proximal, symmetrical, and painless is a hallmark feature of the inflammatory myopathies. Patients with IBM are also prone to distal, asymmetric muscle involvement. Measurement of serum concentrations of muscle enzymes, skin and muscle biopsy, electromyography, and magnetic resonance imaging can assist in the diagnosis. Testing for serum autoantibodies is helpful both in diagnosis and in predicting the clinical phenotype and response to therapy. A minority of patients with DM and PM have myositis that is associated with an underlying malignancy. The risk is greatest for middle-aged to elderly patients with DM. Approximately 15% of DM patients have malignancy-associated disease. Most malignancies present within 1 year before or after the diagnosis of inflammatory myopathy.
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