Histopathological changes in canine allergic contact dermatitis patch test reactions. A study on spontaneously hypersensitive dogs

The histopathology of allergic patch test reactions in dogs with spontaneous allergic contact dermatitis (ACD) was investigated. Epidermal necrosis was present in half of the biopsies and neutrophilic granulocytes were present within epidermis in these biopsies as well as in some of the biopsies without necrosis. Spongiosis was only occasionally observed. Dermal infiltration with neutrophilic granulocytes and oedema was found in all biopsies while the number of lymphocytes was small. The results may indicate a different secretion of or responsiveness towards cytokines in canine ACD compared to ACD in man where epidermal necrosis is not a characteristic feature and where the predominant inflammatory cell is the lymphocyte. It is anticipated that histopathological investigation of patch test reactions in dogs will not be helpful in discriminating between allergic and toxic patch test reactions.