A girl with a solitary red bulla

A 14-year-old girl presented with an asymptomatic giant blister of 2 months' duration on her left shoulder. She reported that the area first appeared as a bruise that subsequently enlarged to form a blister-like lesion. Her medical and family histories were unremarkable. The patient enjoyed outdoor activities but could not recall any inciting trauma. The physical examination revealed a 3.5- × 3-cm erythematous semitransparent bulla overlying a firm and slightly tender nodule (Fig 1). Findings from the histopathologic examination are shown (Fig 2).

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