Erythema multiforme associated with herpes labialis.

1428 CMAJ, November 5, 2013, 185(16) © 2013 Canadian Medical Association or its licensors A35-year-old woman presented to the emergency department with a recurrent rash on the backs of both hands related to what she described as a “fever blister” on her lower lip. In the previous 2 years, she had experienced more than 12 similar eruptions involving both her lip and hands. She was not taking any medications. On examination, the centre of the vesicle on the patient’s lip was yellowish, and the backs of both hands showed red papules and some red plaques with necrotic centres, consistent with target lesions (Figure 1). We diagnosed erythema multiforme secondary to re cur rent herpes labialis. Erythema multiforme is a self-limited hypersensitivity reaction involving both skin and mu cous membranes. The most common condition associated with recurrent erythema multiforme is herpes simplex virus, but a cause cannot be identified in most cases (about 60%). Other known associations with recurrent erythema mul ti forme include complex aphthosis, bacterial infection (e.g., Mycoplasma pneumonia), ad verse drug reactions and menstruation. The lesions of recurrent erythema multiforme typically resolve in 1–2 weeks and are self limited. When associated with herpes simplex virus, the duration of episodes can vary in the same patient and are directly related to intralesional expression of viral genes. When there is mucosal involvement by herpes simplex virus or erythema multiforme, severe symptoms or a high rate of recurrence (as in our patient’s case), treatment and prophylaxis with antiviral agents may be considered. Oral acyclovir has shown to be effective for prophylaxis, with valacyclovir and famciclovir providing alternate options. Antiviral prophylaxis is often effective at preventing erythema multiforme associated with herpes simplex virus. Although other systemic therapies such as azathioprine, dapsone or im mun o globulins have been described, limited evidence supports their efficacy in the treatment of acute episodes. An effective vaccine against herpes simplex virus may eventually prove to be the most desirable intervention.