S1C25P15-3: The interstitial infiltrates of lymphocytes and histiocytes are representative of the lymphohistiocytic collagenosis of morphea. Blue arrows outline a perivascular space containing plasma cells. This combination of features is consistent with changes seen in morphea, but might also be seen as a variation in necrobiosis lipoidica diabeticorum, or lupus profundus. It is tempting to propose that the lymphoid cells of the infiltrates have activated mesenchymal cells (i.e., fibroblasts). As an extension of this approach, the collagenosis with sclerosis would be consistent with a process of immunostimulation. In the area outlined by yellow arrows, the patterns are complex; collagen bundles are variable in size. Some of the thinner bundles are arranged with their long axes parallel to the surface of the skin (streaked in a direction parallel to one another and to the surface of the skin). Some of the thinner bundles partially encircle some of the coarser bundles (pattern of early collagenous ring-binding ). Some of these patterns are acceptable as accretive growth of newly formed collagen bundles at the periphery of pre-existing bundles. In addition, there are zones of pallor in some of the coarse bundles; these zones of pallor may be evidence of fibrolysis or unbundling in anticipation of the interstitial growth of new collagen fibrils in the actual interstitium of the coarse bundles.

S1C25P15-4: The sclerosis of morphea usually is most advanced at the interface between the reticular dermis and the fat. The sclerosing process extends from the original dermal domain into the adipose tissue and, early on, lipocytes may be found among the newly formed collagen bundles. The process incorporates the domain of the adipose tissue as it develops. The fibrous matrix is expanded at the expense of the domain of the lipocytes; one form of connective tissue is substituted for another. The process is a substitutive fibroplasia. In this field, green arrows identify the interface between newly formed fibrous tissue and fat. A vein (blue arrows) shows fibrosis and subintimal infiltrates of lymphocytes. Infiltrates of this type usually contain plasma cells.

S1C25P15-5: A dermal interstitium is easily accommodated in the stores of images for the interpretation of patterns in diseases affecting the reticular dermis. There also is an epithelial interstitium; it provides for metabolic continuity between the dermis and the epidermis. It normally is inconspicuous, but becomes more prominent in certain inflammatory disorders. Spongiosis, as a characterization of a morphologic alteration, gives recognition to an expansion of the epidermal interstitium and, especially, to increased fluidity of a watery type. Such an alteration may be a response that is indicative of the hydrophilic properties of acid mucopolysaccharides. Acid mucopolysaccharides may bind water under the influence of alterations in the chemical and physical environment. In some conditions such as primary lichenoid reactions (disorders in which psoriasiform and lichenoid features are combined in a single lesion), the epithelial interstitium may expand, but may be mucinous rather than watery. The epidermis of lesions of lichen striatus may be focally mucinous (in areas of epidermal hyperplasia with intraepithelial lymphoid infiltrates). Similar changes may be encountered in the follicular component of lichen striatus; the mucinous changes may result in the disruption of intercellular cohesion and the formation of mucin-filled cysts (follicular mucinosis). Follicular mucinosis may be encountered in a variety of clinical settings as a secondary change. In this example, histiocytes and giant cells are present in the mucinous matrix of the follicular epithelial defect; this is a common feature of the infiltrates of follicular mucinosis. Follicular mucinosis might be cited as an additional example of immunostimulation; the lymphoid infiltrates promote the formation of excess mucinous matrix by target cells, the keratinocytes. Even dysplastic lymphocytes may induce this change in follicular epithelium.