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Spongiotic and Psoriasiform Dermatitis (parent chapter for 3 pictorial pages)
The basic pattern in the category of the disorders affecting the superficial reactive unit of the skin is one of inter-cellular edema and epidermal hyperplasia, with both primarily
affecting the basal unit of the epidermis. In this category, the edema generally is most pronounced at the tips of rete ridges. Within such a lesion not all of the supra-papillary domains are affected. In the areas
of epidermal edema, elongated, dendritic histiocytes (Langerhans’ cells) are loosely spaced; they appear to lie within lacunae. Lymphocytes, that have migrated into the areas of edema, seek out the histiocytes; they
often are found in close apposition to them (S2C6P1-1 & 2). The degree of edema is variable but, in areas, the
changes may progress to the formation of a spongiotic vesicle. In these expressed patterns of this immune process, the histiocytes might be characterized as examples of a wandering cell which seeks out foreign
antigens and, in turn, having found them become fixed cells. In close association with the antigens, some of the antigenic material becomes fixed to receptors at the surface of the histiocytes. The histiocyte is
then stimulated to release kinins which promote an inflammatory response, an influx of lymphoid cells. In this sequence, lymphocytes seek out the antigen-bearing histiocytes. The components involved in this type of
a reaction include, in addition to antigen (and antibody, if such is involved): histiocytes (including Langerhans’ cells and migratory, uncommitted histiocytes), lymphocytes (at the cellular level, preponderantly
T-lymphocytes), epidermis (particularly the basal unit), papillary dermis, and the capillary loop of the dermal papillae. In spongiotic disorders, the mucinous interstitium is expanded, but appears watery. This
appearance may be a manifestation of an altered ph and of an promotion of hydrophilia by the expanded matrix. As an example, an expanded, mucinous matrix is seen in the basal unit of a lesion of pemphigus foliaceus (S2P7P2-3); a lesion of pemphigus foliaceus commonly is psoriasiform.
The difference between spongiotic disorders and psoriasiform disorders (with perhaps the exception of psoriasis) basically is manifested in the degree of hyperplasia of the basal unit
of the epidermis. In the psoriasiform disorders, the basal unit hyperplasia is manifested in an accentuation of the rete patterns (S1C6P1-3-7, & S2C7P2-1 & 2).
As the cellular population of the basal unit expands, increased demands are placed on the ability of the capillaries to deliver, and locally release, nutrients into the dermal papillae and, in turn, into the
overlying epidermis. An expansion of the domain of the dermal papillae greatly increases the available epidermal surface along which nutrients can be absorbed; any other accommodation would require an expansion of
the skin surface area, and would result in microscopic convolutions along the surface; in addition, there would be a corresponding increase in the expanse of the superficial unit of the epidermis.
An expansion of the epidermal basal unit is likely to result in a zone of parakeratosis in the overlying keratin layer. This alteration is an expression of an increased rate of
delivery of cells to the superficial unit, a delivery of cells at a rate that exceeds the capacity of the superficial unit to deliver mature keratinocytes to the surface. Instead, the cells have not fully
keratinized at the time of their delivery to the surface; in keeping with a more rapid transfer of cells, there is also a possibility of faulty closure of the intercellular spaces of the superficial unit by lipid
membranes. As a result, the imperviousness of the keratin layer and the superficial unit is compromised. In response to this deficiency, neutrophils are attracted to the superficial unit. They then find their way to
near the surface where they collect, first among viable keratinocytes, particularly those of the granular layer. Having been caught-up in the kinetics of the superficial unit of the epidermis, the neutrophils are
then transferred to the surface in concert with keratinizing cells. There they become collected among the parakeratotic lamellae; these collections form an inspissated pustule (the Munro microabscess).
Not all psoriasiform processes show prominent inter-cellular edema; they may be associated with hyperplastic superficial units and with compact orthokeratinized debris at the surface (S2C7P2-4); terminal differentiation is accentuated in such examples.
Common disorders manifested in spongiotic, or spongiotic and psoriasiform, patterns include contact dermatitis and eczema. Drug eruption, on occasion, may be manifested in spongiotic
and psoriasiform patterns (S2C7P2-5 & 6). Spongiotic and psoriasiform patterns are also a feature of the lesions of
seborrheic dermatitis (S2C7P2-7-8, & S2C9P3-1). Pityriasis rosea is a spongiotic disorder with variable psoriasiform qualities (S2C7aP2a-1 & 2).
Kondo S, Sander DN: Epidermal cytokines in allergic contact dermatitis. J Am Acad Dermatol 1995;33: 786-800.
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