September 2016


Signalment (JPC 2017927):  4-year-old dog   

HISTORY:  The dog was treated for vomiting and diarrhea with trimethoprim-sulfa and prednisolone, and developed sudden onset erythema and sloughing of the epidermis 48 hours after treatment began.

HISTOPATHOLOGIC DESCRIPTION:  Haired skin:  Multifocally within all layers of the epidermis and follicular epithelium, are many individualized and occasionally clustered apoptotic keratinocytes that are shrunken with brightly eosinophilic cytoplasm and pyknotic nuclei, admixed with many viable and degenerate neutrophils and fewer lymphocytes (intraepidermal pustules) that are often clustered around apoptotic keratinocytes (satellitosis). Remaining keratinocytes often exhibit hydropic degeneration. There is rare vacuolation of the basement membrane zone (subepidermal vacuolar alteration) and multifocally the epidermis is separated from the dermis immediately subadjacent to the basal cell layer, forming subbasilar clefts that contain erythrocytes, small amounts of fibrin, and few viable and degenerate neutrophils.  Multifocally infiltrating the superficial dermis, obscuring the dermoepidermal interface and surrounding superficial dermal blood vessels and adnexa, are numerous neutrophils, macrophages, and fewer lymphocytes (interface dermatitis). Dermal fibroblasts are often hypertrophied (reactive), and vessels in affected areas are lined by hypertrophied endothelial cells. Multifocally there is mild epidermal and follicular hyperplasia with thickening of the stratum spinosum (acanthosis), rete ridge formation, intercellular edema (spongiosis) and mild orthrokeratotic hyperkeratosis. 

MORPHOLOGIC DIAGNOSIS:  Haired skin:  Keratinocyte apoptosis, transepidermal and follicular, multifocal, with hydropic degeneration, subepidermal clefting, satellitosis, and neutrophilic and lymphohistiocytic interface dermatitis, breed not specified, canine.

ETIOLOGIC DIAGNOSIS:  Drug-induced dermatosis (historically)

CONDITION:  Erythema multiforme (EM)










Depth of Necrosis



Mucosa and cutaneous; extensive

full epidermal with +/- subepidermal bullae, does not affect dermis

none or minimal except when ulcerated


Glabrous skin of groin and axillae, mucocutaneous, oral mucosa, pinnae, foot pad

full epidermal with numerous apoptotic keratinocytes and +/- subepidermal bullae

lymphohistiocytic, perivascular and interface



coagulative necrosis extends into dermis depending on degree

peripheral neutrophils and macrophages



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