Erythema Multiforme

Erythema Multiforme is a topic covered in the 5-Minute Emergency Consult.

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  • A rash caused by a hypersensitivity reaction:
    • May occur in response to various medications, infections, or other illness
  • Erythema multiforme (EM) minor:
    • Typical target lesions
    • Edematous papules
    • Usually distributed peripherally
    • Benign, self-limited rash generally not associated with acute, serious illness
  • EM major
    • Also called bullous EM
    • Target lesions
    • Edematous papules
    • Also with peripheral distribution
    • Involves 1 or more mucous membranes
    • <10% total body surface area of epidermal detachment
  • Differentiate from:
    • Stevens–Johnson syndrome (SJS):
      • Also <10% TBSA epidermal detachment
      • Often widespread blisters over trunk and face
      • Mucosal involvement
    • Toxic epidermal necrolysis (TEN)
      • >30% TBSA epidermal detachment
    • EM is now considered a different entity from SJS and EM
  • Most often affects children and young adults (>50% younger than 20 yr)
  • Males are affected more often than females.


  • Hypersensitivity reaction, probably transient autoimmune defect
  • Herpes simplex virus (HSV) is the most common precipitant (>70%).
  • Other causes include:
    • Idiopathic
    • Medications
      • Penicillin
      • Sulfur based
      • Phenytoin
      • Barbiturates
      • NSAIDs
    • Vaccines
      • Diphtheria—tetanus
      • Hepatitis B
      • Smallpox
    • Malignancy
    • Infection
      • HIV
      • CMV
      • Hepatitis C
      • Mycoplasma infections

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