Erythema Multiforme

Thanks to Kenny and Chloe for bringing a case earlier this week to ID report of a woman with an HSV infection who had a rash that was either leukocytoclastic vasculitis, erythema multiforme, or maybe both.
Some pearls about EM, something we see rarely in in the inpatient setting.
What is EM?
  • classically a targetoid rash with mucosal involvement. Has a benign clinic course.
  • Called “multiforme” because the rash has protean manifestations. But it classically looks like this:
erythema multiforme.png
  • Rare, most common in children and adults age 20-40.
  • Some more pictures of classic lesions


What causes EM?
  • most commonly HSV-related.
    • rash begins 2-17 days after HSV outbreak
    • recurrent EM is usually HSV-related.
  • Other causes
    • mycoplasma (and other bacterial infections but mycoplasma is common)
    • other viruses
    • malignancy
    • autoimmune disease
    • radiation
    • sarcoid
    • medications
  • Because of the mucosal involvement, it is important to distinguish EM from it’s more life threatening cousin – SJS. Here are some distinguishing feature
    • SJS can atypically have target lesions. The targets of EM are papular, while the targets of SJS are macular
    • Medications rarely cause EM and commonly cause SJS
    • skin sloughing should always make you concerned for SJS
  • Other things on the ddx for targetoid skin lesions
    • urticaria and urticarial vasculitis
    • fixed drug eruption
    • bullous pemphigoid
    • sweets syndrome
    • Rowell syndrome (EM in the setting of cutaneous lupus)
    • cutaneous small vessel vasculitis.
  • Antivirals are helpful if started early in the course of an HSV-mediated outbreak
  • Antivirals do prevent recurrent EM in patients with >6 outbreaks/year
  • topical glucocorticoids (for skin) and glucocorticoid gels (for mucosal involvement) are key for symptomatic relief
  • people with debilitating recurrent EM sometimes need systemic immune suppression. This is rare.
Lamoreux MR1Sternbach MRHsu WT.Erythema multiforme. Am Fam Physician. 2006 Dec 1;74(11):1883-8.

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