Erythema multiforme
Erythema multiforme is an immune-related disorder of the skin and mucous membranes. The most common lesions are erythematous papules and bullae--often a target or iris pattern. EM is usually mild and relapsing with little or no constitutional symptoms. HSV infection precipitates about 75% of cases.
CASES/YEAR
1,500,000 (US); 30,000,000 (Global)
INCUBATION
10-15 days when preceded by an HSV infection; [5MCC-2020]
INITIAL SYMPTOMS
Target lesions of the hands and feet, extensor surface of extremities, and face; Mucous membrane lesions: minimal or absent in EM minor; at least 2 mucosal sites in EM major; [5MCC-2020]
COMMENTS
FINDINGS:
Most common lesions are erythematous papules and bullae--often a target or iris pattern with circles of erythema and normal skin, typically with central vesicle or bulla. [Harrisons, p. 264] EM is usually mild and relapsing with little or no constitutional symptoms. The central zone of the target lesion may be "dusky" or form a blister. Lesions are generally symmetrical and most commonly found on the extensor surfaces (hands, feet, knees, elbows), neck, and face. The oral mucosa is often involved, and the illness usually resolves within 2 weeks. [PPID, p. 805] Lesions are typically dull red macules and papules, resolving within weeks. [Cohen, p. 120] The conjunctiva may be involved. [Guerrant, p. 1001]
PRECIPITATING CONDITIONS:
It is estimated that HSV infection precipitates 75% of cases of erythema multiforme. [PPID, p. 1834] Cancer patients are at increased risk for EM, often caused by herpes simplex virus. [Harrisons, p. 376]
CLINICAL SPECTRUM:
EM minor (mild) < EM major (Stevens-Johnson syndrome) < Toxic epidermal necrolysis (most severe); EM major includes more severe mucosal and skin disease and resembles serum sickness with a 1-14 day prodrome of fever, cough, pharyngitis, vomiting, and fever. Urticarial and purpuric lesions occur in EM major. EM minor resolves in 2-3 weeks. EM major resolves in 3-6 weeks with a 5% mortality rate. Patients with toxic epidermal necrolysis are treated in the intensive care or burn unit and have a mortality rate approaching 30%. [Cecil, p. 2528]
DIAGNOSTIC
Clinical; [Cecil, p. 2628]
SIGNS & SYMPTOMS
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>fever
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E pharyngitis
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E stomatitis
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G diarrhea
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G nausea, vomiting
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O conjunctivitis, acute
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R cough
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S cellulitis or rash, circinate
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S papules or plaques
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S petechiae and ecchymoses
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S rash (exanthem)
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S rash on palms
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S skin blister or vesicles
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S urticaria
TREATMENT
Treat underlying causal disease or discontinue causal drugs. Treat underlying herpes infection with acyclovir or other antiviral, especially if recurrent. Up to 50% of cases triggered by herpes simplex; Disease is self-limited but recurrence rate may be 30%. [5MCC-2020]
REFERENCES FOR CASES/YEAR
1. (US) Annual US incidence <1%; [5MCC-2020] Calculate: 0.005 x 300 million = 1.5 million;
2. (Global) 20 X US cases/yr;