The target lesions on the arm and face led the physician to diagnose erythema multiforme (EM) in this patient. Each target lesion had a small vesicle in the center. The family physician told the parents to stop the antibiotic and recorded an allergy to sulfa in the child's electronic medical record.
EM is considered a hypersensitivity reaction and is often secondary to infections or medications. Herpes simplex viruses (HSVI and HSV2) are the most common causative agents and have been implicated in at least 60% of cases. EM most commonly occurs between the ages of 10 and 30 years, with 20% of cases occurring in children and adolescents.
Classic lesions begin as red macules and expand centrifugally to become target-like papules or plaques with an erythematous outer border and central clearing (iris or bull’s eye lesions). Target lesions, though characteristic, are not necessary to make the diagnosis. The center of the lesion may have vesicles or erosions. Lesions can coalesce and form larger lesions up to 2 cm in diameter with centers that can become dusky purple to necrotic.
Unlike urticarial lesions, the lesions of EM will not fade; once they appear they will remain fixed in place. The lesions may be asymptomatic, although there may be a burning sensation or pruritus. The lesions typically resolve without any permanent sequelae within 2 weeks.
While this patient had no mucosal involvement, it is common for there to be mild involvement limited to one mucosal surface. Oral lesions are the most common, with the lips, gingiva, and palate most often affected.
In this case, once the patient discontinued the antibiotic, the EM cleared spontaneously in a week’s time with no scarring.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Milana C, Smith M. Hypersensitivity syndromes. In: Usatine R, Smith M, Mayeaux EJ, et al., eds. The Color Atlas of Family Medicine. New York, NY: McGraw-Hill; 2009:750-755.
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