ABSTRACT
This chapter examines the histology of scratch-provoked psoriatic lesions, i.e., the H. Koebner phenomenon, in 198 cases of psoriasis and 39 controls. Proliferation of the epidermis has been demonstrated in psoriasis by a variety of methods, most notably by autoradiography. Munro abscesses are a very characteristic feature of well-developed psoriasis plaques. Their mechanism of formation had remained completely obscure. The most distinctive feature of prepinpoint papules was predominantly polymorphonuclear perivascular infiltrates penetrating heavily into the epidermis, as contrasted with the predominance of lymphocytes and macrophages in pinpoint papules. Infiltrates consisting of numerous polymorphonuclear leucocytes and patterns corresponding to those observed after partial stripping were seen in the earliest spontaneously developing lesions. The early histologic changes that precede the development of psoriasis both in lesions provoked by scratching or stripping and in spontaneous lesions are qualitatively comparable to those induced by skin trauma in normal subjects but are quantitatively greater and longer lasting than the latter.
