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.
Dome-shaped, waxy, umbilicated papules
Describes Molluscum contagiosum
Silvery scales on well-demarcated erythematous plaques
Pruritic coin-shaped plaques or grouped vesicles with an erythematous base typically occurring during the cold seasons
Target lesion with variable mucous membrane involvement
Are the most common drug triggers.
Can trigger erythema multiforme minor, but are not the most common cause.
Herpes simplex virus
A common cause, but not the most common.