Polymyositis and dermatomyositis other diagnostic studies

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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]

Other Diagnostic Studies

• Electromyogram may be helpful in the diagnosis of polymyositis and dermatomyositis. Findings suggestive of polymyositis and dermatomyositis include:
  •  Delay in electrical signals between the muscles and nerves when they are stimulated
  • Polyphasic, short, small motor-unit potentials
  • Fibrillation, positive sharp waves, increased insertional irritability
  • Bizarre, high-frequency, repetitive discharges
• Electromyogram may also be used to
  • Identifying active sites of myositis for biopsy
  • Follow up the treatment efficacy. The first sign of improvement in polymyositis and dermatomyositis is the disappearance of fibrillation potentials.
  • Exclude all the other causes of denervations
• Skin biopsy may be used in dermatomyositis,which demonstrates:
  • Poikiloderma
  • Epidermal atrophy
  • Liquefaction degeneration of the basal cells
  • Vascular dilatation
  • Lymphocytic infiltration of the dermis
• Other diagnostic studies for [disease name] include:
  • Histochemical staining, which differentiate polymyositis and dermatomyositis from lower-motor-neuron diseases.
  • Skin biopsy, which demonstrates:
    • [Finding 1]
    • [Finding 2]
    • [Finding 3]