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Psoriasiform Dermatitis
In discussing the most common reaction patterns of the skin, designations, such as spongiotic dermatitis and psoriasiform dermatitis, are considered basic; one designation gives recognition to an alteration in the
fluid interstitium of the epidermis and the other gives recognition to a pattern of epidermal hyperplasia in which the rete patterns are accentuated. This classic approach has utility, if all that is required is an
identification of each of the requisite features. If, on the other hand, an attempt is made to correlate a variety of features, a simple attribution, in which widened inter-cellular spaces become a correlate of an increased amount of fluid in those spaces, may seem to be a limited approach. In fact, an epidermis showing focal widening of inter-cellular spaces is almost invariably hyperplastic (acanthotic). Acanthosis is not as simple a pattern as the usual approach to the definition would imply. It is possible to divide the acanthoses into those that primarily affect the basal unit, those that affect the superficial unit, and those that affect both units of the epidermis. In general, those disorders which are generally spoken of as either spongiotic or psoriasiform are basically acanthoses, primarily affecting the basal unit of the epidermis. If spongiotic and psoriasiform patterns are encountered in a single lesion, the combined patterns are characterized as spongiotic and psoriasiform processes. The two processes are closely related; they often are part and parcel of a single disorder. They probably have sequential relationships. Both processes are generally associated with a widened papillary dermis and with perivenular infiltrates of lymphoid cells in the upper portion of the reticular dermis. The infiltrates follow the vessels into the papillary dermis; they extend along the vessels of the papillary dermis into the dermal papillae. They mostly migrate into the epidermis at the tips of the dermal papillae. It is in these sites that the widening of the spaces among keratinocytes (i.e., edema is the hemodynamic correlate of the morphologic quality of spongiosis) develops. In this sequence, an antigen would have found its way into the epidermis; it would evoke a migration of dendritic histiocytes into the epidermis. The interaction between the two would alter both the fluidity and the ionic character of the epidermal interstitium. The interstitium would become less mucoid and more watery. In response to the cellular and interstitial alterations, lymphoid cells would also find their way into the epidermal interstitium; they would localize in the vicinity of antigen-bearing histiocytes.
Those disorders, which we speak of as spongiotic and psoriasiform, usually are a morphologic manifestation of an immune response to an antigen, or an immune complex. They are an expression of an immune reaction
involving a functioning unit of the epidermis, the reactive superficial unit. Since an alteration in a basic functioning unit is involved in both these histologic categories, it is not surprising that the two
patterns overlap and, in some examples, one may merely be a more extreme expression of the other. In relating patterns to pathways, it may well be that the alterations in the fluidity of the epidermal interstitium
facilitate a migration of lymphoid cells into the epidermis. In the migrations, migratory histiocytes may have a role in producing defects in the basement membrane through which lymphoid cells may follow.
The spongiotic disorders sometimes seem to differ from the lichenoid processes by the extent of damage to the basement membrane zone and by the absence of markers for the coagulative necrosis of individual
keratinocytes (apoptotic debris). The lichenoid reactions are more diffuse at the dermal-epidermal interface; the spongiotic reactions are spotty, often represented in patterns in which one or several papillae,
along with the neighboring expanses of the basal epidermal unit, may be spared among the scattered foci of spongiosis
Kondo S, Sauder DN: Epidermal cytokines in allergic contact dermatitis. J Am Acad Dermatol 1995;33:786-800.
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