S1C23P13-4: The interface reaction is clearly lichenoid. The upward infiltration of lymphocytes and histiocytes into the epidermis, focally, is extensive; the phenomena are somewhat suggestive of a pityriasic variant . In other areas, the basal unit is not as well-developed and lytic changes are most prominent in the basal layer (an erythema multiforme-like quality). In addition, the zone of whorled transepidermal elimination (green arrows) is a feature strongly in favor of a erythema multiforme-like reaction (erythema multiforme).

S1C23P13-5: In this field of the same lesion of erythema multiforme, the lysis of cells is most prominent at the basal layer (i.e., pigmented basal cells). The patterns, if encountered outside the clinical setting of ertyhema multiforme, would qualify as erythema multiforme-like.

S1C23P13-6: In this central area of the same lesion (S1C23P16-4&5), there is marked papillary dermal edema (pattern of so-called dermal variant). A transition to a more characteristic lichenoid pattern is seen to the far right of the field (EM).

S1C23P13-7: Papillary dermal edema is a prominent feature of some biopsy specimens from lesions of erythema multiforme. A transition to a more characteristic lichenoid pattern of erythema multiforme-like type is evident to the extreme left of the field. The green arrows point to two colloid bodies with lymphocytes in close apposition in rosette-like fashion (patterns of this type have been emphasized in description of the histologic changes in experimental cell mediated immune reactions). Disrupted collagen fibers extend into the zone of edema (“swaying in the breeze”).