Polymyositis and dermatomyositis diagnostic study of choice

Muscle biopsy is the gold standard test for the diagnosis of polymyositis and dermatomyositis. Necrosis, increase in endomysial and perimysial connective tissue, atrophy and degeneration of both type I and II fibers, especially in a perifascicular distribution might be seen in muscle biopsy. The muscle biopsy should be performed when a patient presented with symptoms of muscle weakness and skin rash or elevated level of muscle enzymes.

• Muscle biopsy is the gold standard test for the diagnosis of polymyositis and dermatomyositis.^{[1][2][3][4][5]}
• 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.