Erythema multiforme (EM) is a rash with many different forms (which is why it is called "multiforme") and many different causes.  In it's classic form, EM is harmless and will resolve without treatment.  The most recognized EM lesion is a "target lesion," which is a slightly raised, somewhat circular, pink area with a lighter skin-colored center.  EM lesions may also show as bumps or blisters.  The rash often appears all over the body and may change with time.  The cause of EM is different for different cases.  EM may be caused by a virus or medications, but often the cause is not determined.  The rash typically occurs 1-2 weeks after the exposure.  No treatment is necessary for mild cases.  Rarely, EM can be severe (i.e., EM major) but some physicians believe these cases involve a completely different process (i.e., Stevens-Johnson syndrome or toxic epidermal necrolysis).  Lesions within the mouth raise concern for one of these more severe forms.

What is erythema multiforme (EM)?

EM is a rash with many different forms that is likely caused by an overreaction of the immune system to a medication or virus.  The classic skin lesions have a "target" appearance.  These so-called "target lesions" are often raised pink areas with a lighter center.  Target lesions may be small or extremely large (i.e., bigger than a DVD disk).  In most cases no treatment is necessary.

Who can get erythema multiforme (EM)?

Anyone, at any age.  It is probably more common in children versus adults.  The rash most often occurs 1-2 weeks after a medication (i.e., especially antibiotics) or after a viral infection (i.e., especially herpes simplex virus, the "cold sore" virus).

What does erythema multiforme (EM) look like?

EM can have many forms.  The most common form is the target lesion.  The child may first develop welts on the torso, arms, and legs.  These welts may change shape and location over several minutes.  The rash may be extremely itchy or without symptoms.  Welt-like lesions may become pink or red and develop clearing in the center.  This may lead to a "target" appearance with a normal skin area surrounded by a slightly raised pink or red line.  Lesions may have bizarre shapes and join to form larger lesions.  Occasionally the rash may develop blisters, and these blisters may have a circular "doughnut" appearance.  A child with EM should generally appear otherwise healthy.

When should I seek medical care?

Because this rash can be confused with other more serious problems, most cases should be evaluated by a physician.  Some "red flags" that may indicate a serious problem include:

• An ill-appearing child
• Fever
• Poor eating or drinking
• Lethargy 
• Severe rash
• Rash or blisters within the mouth, eyes, or genital area
• Ulcers or large blisters

How is erythema multiforme (EM) diagnosed?

• The physical exam and history usually verify the diagnosis. 
• There is no specific test for EM. 
• A skin biopsy can help with the diagnosis, but this is rarely necessary.

How is erythema multiforme (EM) treated?

• Most cases require no treatment.
• Antihistamines may be used for itching.
• The use of steroids is controversial.
• Skin creams may be helpful.
• Severe cases may require aggressive treatment with hospitalization.

 Photo credit - 1. Alicia Williams en:User:Estreya,2007, WikiMedia Commons. 2. Jmh649, 2009, WikiMedia Commons.

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