Photo Derm Diagnosis: Sudden appearance of erythematous papules and vesicles

A 36 years old man presented with painful erythematous lesions over inner arm and apposing part of trunk for 1 day. He says that he noticed it first in the morning. It was extremely painful (arm trunk) and was associated with burning sensation. He denies use of deodorant or local application of any substance prior to onset of lesions. On examination two lesions were found-one on inner right arm and the other on apposing part of trunk (Figure 1) Inner arm lesion was oval in shape with one narrower end while the trunk lesion was irregular in shape. Individual lesion comprised of multiple erythematous papules and few vesicles surrounding an area of necrosis (blackish area). Skin necrosis was more pronounced in arm lesion than in trunk lesion (Figure 2). Rest of the cutaneous examination was unremarkable.