Iatrogenic benign lymphoplasia induced by allergic contact dermatitis from squaric acid dibutylester: immunohistologic study of cellular infiltrates.

We report of a 62-year-old male patient with a dull red itchy nodule on the induction area of allergic contact dermatitis to squaric acid dibutylester, which had been used for the therapy of alopecia universalis. The excised biopsy specimen showed dense infiltration of lymphoid cells in the dermis and subcutaneous tissue, associated with the formation of lymphoid follicles. Immunohistologic analysis of the infiltrates indicated mixed proliferation of T- and B-cells. A biopsy specimen from the challenge area showed spongiosis in the epidermis and lymphoid cell infiltration in the upper dermis, while the infiltrates consisted mainly of T-cells. The following points are discussed: (i) the lesion had an iatrogenic origin and the causative agent was quite evident; (ii) the route of allergen application was only through the epidermis and not directly in the dermis; (iii) lymphoid cell infiltrates of the induction and challenge areas were different.