Ch 25 Dermal-Epidermal Junction

Buster (the plight of feral cats)

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Fig. 1(Ch25) (104478): At high magnification, the basal layer is not well defined and many of the basal keratinocytes show dyskeratotic changes. There is an increased number of clear cells in the basal layer. Some of the lacunar dendritic cells above the basal layer are interpreted as dendritic histiocytes (Langerhans cells). The papillary dermis shows lamellar fibrosis (vertically oriented lamellae) and scattered dendritic melanophages. A basement membrane is not well defined. The rete ridge is thin; on the right, there is a cleft at the D-E interface.

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Fig. 2 (Ch25) (104478): A clearly defined basal layer is not a feature. Keratinocytes that abut upon the papillary dermis have their long axis parallel to the surface of the skin; many of these cells show dyskeratosis with brightly acidophilic cytoplasm. Just above the center of the field, there is an angulated cleft at the D-E interface. This may represent a late stage in an erosive process involving a rete ridge. Some of the keratinocytes, at or above the basal layer, are pigmented. Pigmented, dendritic melanophages are present in the papillary dermis. The upper portion of the dermis is fibrotic; the pattern of the collagen bundles is abnormal.

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Fig. 3 (Ch25) (104478): A basal layer is not well defined; there are spotty areas of liquefaction degeneration at the D-E interface. A basal unit mostly is represented only in the rete ridges. Many of the basal keratinocytes and some of the cells in the basal unit show dyskeratosis. Rete ridges are short and thin. There are scattered melanin deposits in the fibrotic papillary dermis. A basement membrane is not well defined. Some of the cells in the altered papillary dermis are dendritic in outline. There is mild melanocytic hyperplasia.

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Fig. 4 (Ch25) (104478): The epidermis shows a prominent granular layer and hyperplasia of the superficial unit of the epidermis. The basal unit is thin and shows cellular disarray, peri-nuclear vacuoles, and dyskeratosis. Yellow arrows identify basal dendritic cells (melanocytes). The basement membrane is poorly defined but pale and coarsened (hyalinized). Scattered small defects at the D-E junction contain histiocytes and lymphoid cells. A blue arrow identifies a migratory histiocyte near the D-E junction. Green arrows identify basal keratinocytes with increased cytoplasmic acidophilia extending to the basement membrane. In a cleft at the D-E interface near the left margin, lymphocytes and histiocytes have clustered. The cells of the superficial unit of the epidermis are individual enlarged; they have enlarged nuclei, and prominent nucleoli; there are peri-nuclear vacuoles. In irregular defects in the superficial unit, a dendritic histiocyte (Langerhans cell) is in close apposition to one or two lymphoid cells; the patterns are consistent with patterns seen in immune diseases in which histiocytes have a role in the presentation of antigens. Lymphocytes are sprinkled among histiocytes and dendritic fibroblasts of the dermis. A vessel in the right lower corner has a hyalinized wall. Collagen bundles are coarsened and the pattern of the bundles is abnormal.

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Fig. 5 (Ch25) (104478): The basal layer shows atypical hyperplasia of dendritic cells. Yellow arrows identify keratinocytes showing dyskeratotic changes. Blue arrows identify a coarsened basement membrane. Above and just to the left of the center of the field, a membranous loop enclosed a single cell with delicate cytoplasmic processes. An abnormal fibrous matrix extends to the basement membrane. Dendritic cells in the dermis are interpreted as fibroblasts.

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