Parents pay a lot of attention to the skin of their child and, certainly, the skin exam is a valuable tool for the vigilant clinician (ex, Cap Refill, Petechiae below Nipple Line, Leukemia, RMSF). That being said, the majority of pediatric rashes (See Peds Rash) that present to the ED are often met with a combination of disdain and fear: “This looks like nothing, but is it something?” or “This looks awful, but is it a big deal?” One of the concerning characteristics is the target lesion, but not all target lesions are created equal. Let us take a minute to digest a morsel on Erythema Multiforme (EM).

Erythema Multiforme: Basics

• Erythema multiforme is the skin manifestations of an acute immune-mediated reaction.
• The immune-mediated reaction is often triggered by:
  • Viral infection – Majority of cases.
  • HSV infection
  • Mycoplasma pneumonaie
  • Medications 
    • In children, medications are more closely related to SJS and TEN.
    • Adults have a stronger association of EM with medications.
  • Immunization [Read, 2015]

• Erythema multiforme is typically self-limited.
• Often it is considered to be on the spectrum that includes Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), but…
  • Current classification distinguish EM from this specific spectrum. [Bastuji-Garin, 1993]
  • Erythema Multiforme differs from SJS, SJS-TEN Overlap, and TEN in: [Auquier-Dunant, 2002]
    • Demographic characteristics
    • Risk factors
      • It is not associated with HIV infection, cancer, or collagen vascular diseases.
      • It has less of an association with medications.

Erythema Multiforme: Mimics

• Erythema multiforme in children is often misdiagnosed. [Read, 2015; Léauté-Labrèze, 2000]
• Target lesions are NOT pathognomonic for erythema multiforme. [Read, 2015]
• There are several other conditions that need to be considered when evaluating target lesions:
  • Serum Sickness
  • Kawasaki Disease
  • HSP
  • Lupus Ertyhematosus
  • Urticaria multiforme
    • Often mistaken for erythema multiforme. [Read, 2015]
      • Acute urticaria that are annular and polycyclic wheals
      • Have central clearing and ecchymotic centers
      • Typically start as small macules or papule and then evolve to various sizes.
      • Individual lesions fade within 24 hours.
    • NOT fixed to the extremity distribution like EM is.
      • Involves trunk, face, and extremities.
    • Patient may also have pruritus, angioedema, and/or dermatographism (which is pretty interesting to see).

Erythema Multiforme: Diagnosis

• The classification criteria for EM are based on Bastuji-Garin, 1993.
• When observing lesions, consider location and document what you see… don’t just say “target lesions”… make note of all characteristics when able (something I am terrible at).
  • EM Minor
    • Epidermal detachment < 10% BSA
    • Acrally distributed lesions (acral = extremities, ears, peripheral parts)
      • Can be typical or raised atypical or combination of lesions
      • Typical Target Lesions = <3cm diameter, symmetric, round, well-defined border, and 3 concentric color zones
      • RAISED Atypical Target Lesions = <3 cm diameter, round, poorly defined border, only 2 concentric color zones.
    • No mucosal involvement
      • EM Major is the same as EM minor but has one or more mucosal surface involved.
  • SJS and TEN
    •  Lesions are different:
      • Flat, atypical target lesions or
      • Widespread macules
    • Amount of Epidermal detachment determines classification
      • SJS has <10% BSA
      • SJS/TEN Overlap has 10% – 30% BSA
      • TEN has >30% BSA

Erythema Multiforme: Management

• Treatment is supportive.
• Symptomatic care with antipyretics and antihistamines can help.
  • There have been reported concerns that NSAIDs may worsen the condition. [Dore, 2007]
• If there is a clear association with a medication, cessation of that is warranted.
• Majority of children with erythema multiforme are able to be discharged and managed as outpatients. [Read, 2015]

Moral of the Morsel

• Distribution matters. If it involves more than the extremities, think twice about calling it erythema multiforme.
• Not all target lesions are the same. Flat, atypical targets are not consistent with EM.
• Think about urticarial multiforme. Just another odd condition to keep in mind to ensure we are not misclassifying illnesses.
• Think worse first! Look for the mucosal membrane involvement closely!

References