S4C14P6-2: Lesions of post-herpetic erythema multiforme.

S4C14P6-4: This lesion, in the clinical setting of post-herpetic erythema multiforme, shows prominent cytopathic changes including ballooning degeneration and coagulation of keratinocytes. In addition, there are lytic defects in reticulated patterns. The clusters of nuclei (blue arrows) suggest the nuclei of giant cells, although they are not associated with intact cytoplasm. These nuclei show central areas that are homogenous and faintly acidophilic. These nuclear changes are of a type commonly seen in the dying cells of a herpes virus infection. These findings, in a lesion of post herpetic erythema multiforme suggest the possibility of a viral infection.

S4C14P6-5: This lesion of erythema multiforme shows the cytopathic changes of a herpes virus infection, but intranuclear inclusions are not a feature. A defect in the basal unit is outlined by red arrows. It contains histiocytes, lymphocytes, and necrotic keratinocytes. It might be characterized as the nidus about which regenerating keratinocytes will form in the early stages of whorled transepidermal elimination . At the right-hand margin of the field, the cytopathic changes qualify as reticulated vesiculation (vertically oriented, angulated defects among elongated keratinocytes).

S4C14P6-6: This lesion of herpes simplex infection shows many of the features seen in the lesion of erythema multiforme in figure S4C14P6-5. In the area outlined by blue arrows, the patterns are distinguished by a multinucleated giant cell and by the nuclear characteristics of the giant cell (i.e., intranuclear inclusions ). In the area outlined by green arrows, ballooning degeneration is a prominent feature. The eventual disruption of these distended, balloon cells leads to the formation of a vesicle that is reticulated (angulated defects rather than the rounded defects of spongiotic vesiculation). A few neutrophils are present in the epidermis just below the multinucleated giant cell.