Histological, Immunohistochemical and Ultrastructural Aspects of Contact Dermatitis

Histological diagnosis of allergic contact dermatitis is extremely difficult since the variability of morphologic patterns and the timing of biopsy. The histological findings that best describe this type of dermatitis are spongiosis that eventually leads to the formation of vesicles and bullae, and a mild perivascular inflammatory infiltrate made of mononucleated cells. In chronic forms, acanthosis and hyper-parakeratosis of epidermis predominate. Immunohistochemistry and ultrastructural pathology may give additional information. Differential diagnosis with other dermatosis must be accurately made since there are multiple variants of allergic dermatitis. Irritant contact dermatitis is histologically characterized hyper-parakeratosis, spongiosis, acantholysis and in more severe forms by bullae and neutrophilic infiltration. As for the differential diagnosis between allergic and irritant dermatitis the biopsy is of little help because lack of specificity but the occurrence of follicular spongiosis, lymphocytic exocytosis of the follicular infundibulum best characterize the allergic forms, especially in early phase; the presence of epidermal necrosis and dermal infiltration of neutrophils are in favour of irritant dermatitis.