Diagnosis: Erythema multiforme

Erythema multiforme is a self-limited disease that often occurs in young adults. It often presents as fixed erythematous papules that evolve into classic lesions with a central dusky area and a paler surrounding area that resemble a “target” or “bullseye.” They may appear raised or edematous. The palms, soles, and upper extremities are most commonly affected, although other areas can be involved.

Although the pathophysiology is not completely understood, 50% of patients report a preceding herpes simplex infection, most commonly labial, by 3-14 days. Other infections that may precede erythema multiforme include orf, histoplasmosis, and the Ebstein-Barr virus; 50% of cases are idiopathic, with no precipitating factor identified. 

Erythema multiforme is often diagnosed clinically. The differential diagnosis includes urticaria, subacute cutaneous lupus erythematosus, fixed drug eruptions, viral exanthems, and granuloma annulare. In difficult cases, histopathology may be helpful and could reveal apoptotic keratinocytes, a lymphocytic infiltrate at the dermal-epidermal junction and around dermal blood vessels, and occasional exocytosis of lymphocytes.

Treatment of erythema multiforme includes symptom relief for pruritic lesions with oral antihistamines. Acyclovir may be beneficial as prophylaxis for individuals with frequent recurrences of HSV and erythema multiforme. Oral corticosteroids are not advised.