Diagnosis: Necrotic Keratinocytes
• Erythema multiforme, fixed drug eruption, and graft-versus-host disease can be virtually indistinguishable histologically from one another. They are classified as interface dermatitides with a predominantly lymphocyte infiltrate and necrotic keratinocytes in the epidermis.
• Fixed drug eruptions sometimes can be distinguished from erythema multiforme by the deeper extension of the infiltrate, the presence of a few neutrophils, and more prominent pigment incontinence.
• Acute graft-versus-host disease has been classified into four histopathologic grades: grade I, basal vacuolar change; grade II, dyskeratotic cells in the epidermis or follicle and dermal lymphocytic infiltrate; grade III, subepidermal cleft formation; and grade IV, complete loss of the epidermis.
• The histologic appearance of erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis may appear identical. Generally, erythema multiforme shows less epidermal necrosis, more dermal inflammation, and exocytosis, whereas Stevens-Johnson syndrome and toxic epidermal necrolysis reveal more epidermal necrosis and less dermal inflammation. However, because of the overlapping histologic features, clinical correlation is required for a final diagnosis.
• Satellite cell necrosis (a dyskeratotic keratinocyte surrounded by two or more epidermal lymphocytes) can be seen not only in graft-versus-host disease but also in the eruption of lymphocyte recovery, erythema multiforme, paraneoplastic pemphigus, regressing verrucae plana, and drug reactions.
