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…
Typical (<3cm, round, symmetric, well-defined, 3 concentric zones)
Atypical (raised, <3cm, round, poorly defined, only 2 concentric zones)
A combination of both
Usually a self-limiting condition with no complications, it affects both young adults (under 40) and children (20% of cases).
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.
Many thanks to Dr Lisa Keillor for peer reviewing this topic!