Lightning Learning: Erythema Multiforme

Lightning Learning: Erythema Multiforme


Erythema Multiforme (EM) is a Type 4 hypersensitivity reaction. It is known for causing characteristic target lesions.

NB: Target lesions are not pathognomonic for EM – remember to consider other causes

Skin lesions are usually acute in nature (24-48 hours) with little or no prodromal illness. They are acrally distributed (e.g. ears, extremities) and can be either…

  1. Typical (<3cm, round, symmetric, well-defined, 3 concentric zones)

  2. Atypical (raised, <3cm, round, poorly defined, only 2 concentric zones)

  3. A combination of both


Usually a self-limiting condition with no complications, it affects both young adults (under 40) and children (20% of cases).

Causes include:

  • Infection (90%) – most common herpes simplex virus (50%), can develop recurrence

  • Medication (10%) – most often penicillin and NSAIDs

If symptoms are more severe and patient is unwell consider Stevens-Johnson syndrome (SJS) or Toxic Epidermal Necrolysis (TEN). Get senior help & discuss with ITU early.


The TWO Types of EM

EM Minor: does not involve mucosa

EM Major: as described in STOP! Involves one or more mucosa (e.g. eyes, GU, GI tract)

Many thanks to Dr Lisa Keillor for peer reviewing this topic!
Lightning Learning: TAPVD

Lightning Learning: TAPVD

#SimBlog: A Tiny Surprise

#SimBlog: A Tiny Surprise