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Updated: Feb 28 2022

Erythema Multiforme

  • Snapshot
    • A 12-year-old girl was recently treated for walking pneumonia and was found to be positive for mycoplasma. A few days into her illness, she developed multiple raised lesions over her palms, back of hands, and extensor forearms. These lesions were targetoid and mildly itchy. There were no lesions on her mucous membranes.
  • Introduction
    • Hypersensitivity reaction of the skin
      • Inflammation and cell death secondary to macrophage and CD8 T lymphocyte influx
    • Common, acute, mucocutaneous disease with classic target-shaped lesions in a symmetric distribution
    • Causes
      • most common = infection
        • Herpes simplex
        • Mycoplasma pneumonia
        • upper respiratory infections
      • less common = drugs
        • e.g., sulfonamides, β-lactams, phenytoin
      • idiopathic
    • Often affects young adults (18 - 30 years old especially)
    • Distinct from SJS/TEN, which is amore severe mucocutaneous reaction that is usually caused by a medication
  • Presentation
    • Skin exam
      • raised (papular), target lesions with multiple rings and dusky center (in contrast to annular lesions, as in urticaria)
        • three concentric zones of color from center to outer ring
          • central dusky/dark area that can be crust or vesicle
          • paler pink or edematous zone
          • peripheral red/dark ring
      • negative Nikolsky sign (as opposed to SJS/TEN)
      • most commonly involves
        • palms/soles
        • backs of hands and feet
        • extensor aspects of forearms and legs
    • May involve mucous membranes
    • May have systemic signs
  • Evaluation
    • Based on symptoms and clinical history
      • recent history of infection can aid diagnosis
  • Differential Diagnosis
    • SJS/TEN (flat lesions, tender, always with mucous involvement, + Nikolsky sign)
    • Urticaria (annular lesions)
    • Erythema nodosum
    • Viral exanthems
  • Treatment
    • Supportive care
    • Corticosteroids if severe
    • Treat underlying cause if identified
      • oral acyclovir for HSV
  • Prognosis, Prevention, and Complications
    • Prognosis
      • typically self-limited
    • Prevention
      • treat chronic herpes infections
    • Complications
      • usually none
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