Rheumatology Question 17 Instructor

What are the 5 major diagnostic features of polymyositis and dermatomyositis?

  • Proximal muscle weakness
  • Myopathic features on EMG testing
  • Elevated muscle enzymes (Primarily the CK, though elevations of AST and LDH are also seen).
  • Presence of a typical skin rash (in the case of dermatomyositis)
  • Positive muscle biopsy (note that the histological features of PM and DM are different. PM is characterized by endomyseal infiltration of inflammatory cells, most of which are CD4+ cells. In DM, an inflammatory infiltrate is seen in the perivascular and perifascicular regions).

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