A jet-black lesion with ragged borders

Over a three-month period, a 57-year-old man developed pruritic urticarial patches over his trunk and limbs (Figure 1). The individual lesions would persist for days to weeks and often coalesced to form plaques. Skin biopsy showed an epidermis that was covered by a loose stratum corneum. There was focal separation of keratinocytes (spongiosis), and the upper dermis showed a perivascular interstitial infiltrate of lymphocytes as well as numerous eosinophils. An early subepidermal cleft was visible (Figure 2).