What is the role of electromyography in the workup of polymyositis?

Updated: Jun 13, 2020
  • Author: Mythili Seetharaman, MD; Chief Editor: Herbert S Diamond, MD  more...
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Answer

Electromyographic findings are abnormal in almost all patients (90%) with polymyositis. Various abnormalities consistent with polymyositis may be found, depending on the stage of disease. In patients with inclusion body myositis myopathic and neuropathic changes may be present:

  • Evidence of membrane irritability, increased insertional activity, fibrillation potentials, positive sharp waves at rest

  • Myopathic changes of motor unit action potential; decreased amplitude and duration; increased polyphasic potentials; bizarre, high-frequency, repetitive discharges

  • Chronic changes, evidence of denervation-reinnervation


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