PANCE Blueprint Dermatology (5%)

Erythema multiforme (ReelDx)

REEL-DX-ENHANCED

Erythema Multiforme

Patient will present as → a teenager with bilateral symmetrical red papular rash with many target lesions confined to both lower limbs of one week duration. The rash appeared few days after herpes facialis.

Erythema multiforme (EM) is an acute, self-limited hypersensitivity reaction.

  • Mostly (∼90% of cases) triggered by infectious agents (up to 50% by herpes simplex virus [HSV]-1 or -2) or, less commonly, by drugs.
  • Involving the skin and the mucous membrane, most commonly the mouth (60–70% of all patients with EM have oral lesions)
  • Skin lesions include raised typical target or “iris” lesions or raised atypical lesions predominantly involving the extremities. Target-like shape, blanching, and lack of itchiness help characterize this rash!
  • 2 subtypes, erythema multiforme minor (EMm) and erythema multiforme major (EMM), with the former involving none or 1 mucous membrane, and the latter involving at least 2 mucous membrane sites
  • Flat, atypical lesions and macules with or without blisters are more suggestive of Stevens-Johnson (SJS) or toxic epidermal necrolysis (TEN).

EM may appear similar to Steven Johnson Syndrome (SJS) but SJS has a more generalized distribution of lesions; concentrated on the trunk (EM extremities and mouth), an absence of raised typical target lesions and atypical flat (not raised) target lesions or macules with coalescence of lesions.

Diagnosis is based on absent or mild prodromal symptoms, preceding HSV infection (up to 50% of cases) 10–15 days before the skin eruptions and a rash involving the skin and sometimes the mucous membrane, most commonly the mouth.

Treatment of any underlying or causative disease

  • Withdrawal of any drugs that might be the cause
  • Symptomatic treatment with oral antihistamines and topical corticosteroids for mild cases; mouthwashes or topical steroid gels for oral disease
  • Early treatment with acyclovir may lessen the number and duration of cutaneous lesions for patients with coexisting or recent HSV infection.
    • Acyclovir for adults: 200 mg, 5× a day for 7–10 days in the onset of EM
    • For pediatric patients: 10 mg/kg/dose TID for 7–10 days
  • Prednisone for severe cases.
Erythema multiforme

Erythema multiforme

Question 1
Which of the following best describes erythema multiforme?
A
Dome-shaped, waxy, umbilicated papules
Hint:
Describes Molluscum contagiosum
B
Silvery scales on well-demarcated erythematous plaques
Hint:
Psoriasis
C
Pruritic coin-shaped plaques or grouped vesicles with an erythematous base typically occurring during the cold seasons
Hint:
Nummular eczema
D
Target lesion with variable mucous membrane involvement
Question 1 Explanation: 
Erythema multiforme presents as target lesion with variable mucous membrane involvement.
Question 2
The most common cause of erythema multiforme minor is
A
Sulfonamides
Hint:
Are the most common drug triggers.
B
Fungal infections
Hint:
Can trigger erythema multiforme minor, but are not the most common cause.
C
Herpes simplex virus
D
Mycoplasma species
Hint:
A common cause, but not the most common.
Question 2 Explanation: 
Herpes simplex virus is the most common cause of erythema multiforme minor. Approximately 90% of cases of erythema multiforme minor follow outbreaks of herpes simplex.
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