S2C4VA1Reactions

Inflammatory Diseases (reaction patterns)

1. reactions mediated at the level of the Langerhans cell

a. spongiotic dermatitis

b. psoriasiform dermatitis

c. spongiotic and psoriasiform dermatitis

S2C4VA1-1: Three distinctive histiologic reaction patterns associated with immune reactions at the level of the Langerhans cell are listed. These are basically proliferative variants with little evidence of lysis and coagulation of target cells (i.e., keratinocytes of the basal unit of the epidermis). In addition, these three patterns are the most common reactions involving the reactive superficial unit of the epidermis (i.e., the epidermis and the papillary dermis, and related lymphohistiocytic components). The immunologic relevance of this approach, in the definition of reaction patterns, is greater than that of the commonly cited approach in which emphasis is placed primarily on the distribution of lymphoid infiltrates along dermal vessels. Generally, I find that a resident, having characterized a histologic pattern by giving primary attention to the distribution of infiltrates along dermal vessels (i.e., as superficial, deep, or both) is at a loss to do much with the characterization and must then search out other features.

S2C4VA1-2: The concept of a reactive superficial unit mostly gives recognition to the interplay that is involved, between epidermis and papillary dermis, in response to immune reactions mediated at the level of the epidermal Langerhans cell.

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Basic Reaction Patterns

1. reactive superficial unit (examples):

a. psoriasis (and psoriasiform processes)

b. neurodermatitis and nummular eczema

c. lichen simplex chronicus

d. contact dermatitis

e. pityriasis rosea

f. mild T-cell dysplasias

g. seborrheic dermatitis

h. PUPP

i. EAC (superficial variant)

j. superficial fungus infections

S2C4VA1-3: Examples of disorders, in which histologic patterns are spongiotic, or spongiotic and psoriasiform, are listed.

S2C4PVA1-4: Cells of the basal epidermal unit and of the superficial epidermal unit are diagramatically represented. If a plane is visualized as passing through the word “KINETICS” and, if then, that plane is assumed to be parallel to the skin surface, the long axis of the small rectangular cells might be characterized as being perpendicular to the skin surface. The two small rectangular cells diagramatically represent basal cells of the basal unit of the epidermis; they are vertically oriented with respect to the skin surface. On the other hand, the plump spindle cells diagramatically represent cells of the superficial unit of the epidermis. With the virtual orientation as described above, their long axis is parallel to that of the skin surface (and the basement membrane).

Basal keratinocytes (i.e., cells of the basal unit and not simply cells of the basal layer of the epidermis) are concerned, in part, with maintenance of the basement membrane and with its integrity. The transport of metabolites into the mucinous avenues of the epidermis is, in large part, a function of both an intact basement membrane and basal keratinocytes. The basal unit is a store, the cells of which readily enter the cycle of dividing cells. The cells of the superficial unit, in a physiologic form of death (i.e., terminal differentiation), provide an impervious barrier at the surface to the skin. There is progressive movement of cells of this unit to the surface; this movement is invariably an act of dying (terminal differentiation). As part of the implementation of imperviousness along the surface of the superficial unit, the component cells, concomitant with the process of terminal differentiation, release kertinosomes (Odland bodies) into, and close off, the inter-cellular avenues. The bodies are the source of material that forms into a lipid membrane among the dying, keratinizing cells - cells that are in transit to the surface of the skin. The epidermis thus is compartmentalized with each compartment having a specific role. An alteration in the kinetics of the basal unit will be reflected in an alteration in the histologic patterns in, and functions of, both the basal and the superficial units. In response to cell-mediated injury of basal keratinocytes, the keratin layer at the surface becomes either parakeratotic (increased turnover, or turnover of cells at a more rapid rate), or it becomes compacted and thickened (compact hyperkeratosis [hyper-orthokeratosis]).

S2C4VA1-5: In the evolution of spongiotic changes in the epidermis, the primary nidus usually appears to be a dendritic histiocyte in a lacunar pattern (the cells appear to lie in lacunae among the keratinocytes). Lymphocytes and migratory histiocytes are attracted to these cells in certain cell-mediated immune reactions and, in the process, the pattern of interstitial epidermal edema extends along the neighboring intercellular avenues. Lymphocytes and migratory histiocytes are attracted to the widened intercellular spaces (areas of edema or spongiosis). In more severe examples of this reaction, the fluid component progressively distends the lacunae and inter-cellular avenues, eventually disrupting the cohesive forces among the neighboring keratinocytes. The pressure of the expanding fluid medium compresses the neighboring epidermis to produce a symmetrically rounded space, the spongiotic vesicle. Acid mucopolysaccharides of the epidermal interstitium have the capacity to become hydrophilic in response to local ionic alterations. This ability to attract fluid probably is instrumental in producing the the expansion of the epidermal interstitial matrix in inflammatory disorders.

Spongiotic Dermatitis

1. a basic reaction pattern in response to a variety of antigens of both internal and external origin

2. the settings include contact dermatitis, eczema, and some drug eruptions

3. a characteristic pattern of many of the “pityriasic” disorders

S2C4VA1-6: Clinical and immune associations of spongiotic disorders.

S2C4VA1-7: Although this visual aid was designed to portray stages in the evolution of the lichenoid reactions, the changes in the “primary” stage, as illustrated to the left in this drawing, have relevance in arriving at an understanding of the alterations in the reactive superficial unit of the skin in the evolution of the psoriasiform disorders (spongiotic and psoriasiform disorders are commonly part and parcel). Normal relationships in the functioning units of the epidermis are pictured to the far left in the drawing. The cells of the basal unit of the epidermis are blue; those of the superficial unit are pale red. The keratinized lamellae at the surface of the skin are loosely collected in “basket-weave” patterns. A line separates the basal and superficial units. The papillary dermis is yellow and the dermal papillae are short and blunt. Blue cells of the basal unit tend to have their long axes perpendicular to both the surface of the skin and the basement membrane. The pale red cells of the superficial unit tend to have their long axes parallel to the surface of the skin. Often, the initial expression of an inflammatory reaction in the skin is hyperplasia of the basal unit of the epidermis and, in response, the superficial unit becomes compromised. It becomes thinner with fewer cell layers represented. It is basic to basal unit hyperplasia that, if the stimulus is sufficient, the expanding basal unit, experiencing an increase in the need for blood-borne metabolites, can only find compensation by accentuating the width and length of the rete ridges and, in turn, by a lengthening of the dermal papillae. We tend to speak of these compensations as psoriasiform qualities. In this drawing, the “primary” patterns are psoriasiform; there is parakeratosis at the surface.

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