How is polymyositis characterized?

Updated: Jan 05, 2021
  • Author: Mythili Seetharaman, MD; Chief Editor: Herbert S Diamond, MD  more...
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Polymyositis is an idiopathic inflammatory myopathy characterized by the following [1] :

  • Symmetrical, proximal muscle weakness
  • Elevated skeletal muscle enzyme levels
  • Characteristic electromyography (EMG) and muscle biopsy findings (see the images below).
Polymyositis. MRI of thighs showing increased sign Polymyositis. MRI of thighs showing increased signal in the quadriceps muscles bilaterally consistent with inflammatory myositis.
Polymyositis. Histopathology slide shows endomysia Polymyositis. Histopathology slide shows endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.

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