Polymyositis and dermatomyositis diagnostic study of choice

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]

Diagnostic Study of Choice

• Muscle biopsy is the gold standard test for the diagnosis of polymyositis and dermatomyositis.
• The following result of muscle biopsy is confirmatory of polymyositis and dermatomyositis:
  • Necrosis
  • Phagocytosis
  • Regenerative activity reflected by basophilia, large, vesicular nuclei and prominent nucleoli
  • Atrophy and degeneration of both Type I and II fibers, especially in a perifascicular distribution
  • Internal migration of nuclei
  • Vacuolization
  • Fiber-size variation
  • Mononuclear inflammatory infiltrate, often most prominent in a perivascular location
  • Increase in endomysial and perimysial connective tissue
• The muscle biopsy should be performed when:
  • The patient presented with symptoms of muscle weakness and skin rash
  • An elevated level of muscle enzymes is detected in the patient.