Idiopathic Inflammatory Myopathies

Idiopathic Inflammatory Myopathies is a topic covered in the Washington Manual of Medical Therapeutics.

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General Principles

Idiopathic inflammatory myopathies are a group of heterogeneous disorders characterized by inflammation of the skeletal muscle. These can be differentiated by the pattern of muscle involvement, extramuscular manifestations, specific serologies, and findings on muscle biopsy.

Classification

  • Dermatomyositis (DM): inflammatory myopathy associated with proximal muscle weakness and a characteristic skin rash. DM includes clinically amyopathic dermatomyositis (CADM) and juvenile-onset DM.
  • Polymyositis (PM): inflammatory myopathy that presents as proximal weakness and occasionally tenderness of the proximal musculature but lacks characteristic rash.
  • Overlap syndromes: Inflammatory myopathy that occurs in the setting of another systemic rheumatic disease (i.e., SLE, systemic sclerosis, etc.).
  • Anti-synthetase syndrome is a spectrum of inflammatory myopathies defined by the presence of an antibody directed against one of several aminoacyl-transfer RNA (tRNA) synthetases.
  • Inclusion body myositis (IBM): inflammatory myopathy that commonly involves distal musculature and has specific muscle biopsy findings.
  • Immune-mediated necrotizing myositis (IMNM): this inflammatory myopathy resembles PM, but muscle necrosis and minimal inflammatory infiltrate seen on muscle biopsy distinguish it from PM.

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General Principles

Idiopathic inflammatory myopathies are a group of heterogeneous disorders characterized by inflammation of the skeletal muscle. These can be differentiated by the pattern of muscle involvement, extramuscular manifestations, specific serologies, and findings on muscle biopsy.

Classification

  • Dermatomyositis (DM): inflammatory myopathy associated with proximal muscle weakness and a characteristic skin rash. DM includes clinically amyopathic dermatomyositis (CADM) and juvenile-onset DM.
  • Polymyositis (PM): inflammatory myopathy that presents as proximal weakness and occasionally tenderness of the proximal musculature but lacks characteristic rash.
  • Overlap syndromes: Inflammatory myopathy that occurs in the setting of another systemic rheumatic disease (i.e., SLE, systemic sclerosis, etc.).
  • Anti-synthetase syndrome is a spectrum of inflammatory myopathies defined by the presence of an antibody directed against one of several aminoacyl-transfer RNA (tRNA) synthetases.
  • Inclusion body myositis (IBM): inflammatory myopathy that commonly involves distal musculature and has specific muscle biopsy findings.
  • Immune-mediated necrotizing myositis (IMNM): this inflammatory myopathy resembles PM, but muscle necrosis and minimal inflammatory infiltrate seen on muscle biopsy distinguish it from PM.

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