Erythema Multiforme

Basics

Description

  • 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:
    • 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 distinct from SJS and TEN
  • Most often affects children and young adults (>50% younger than 20 yr)
  • Males are affected more often than females

Etiology

  • Hypersensitivity reaction, probably transient autoimmune defect
  • Herpes simplex virus (HSV) is the most common precipitant (>70%)
  • Other causes include:
    • Infection:
      • Mycoplasma
      • HIV
      • CMV
    • Hepatitis C medications:
      • Sulfa drugs
      • Anticonvulsants
      • Antibiotics
    • Vaccines:
      • Diphtheria–tetanus
      • Hepatitis B
      • Smallpox
    • Malignancy
    • Idiopathic

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