S13C14P12Porokeratosis

S13C14P12-1: Porokeratosis is a clonal disease of the epidermis. In addition, the clone often is recognized by the host immune response, particularly in the disseminated actinic variant; a lichenoid pattern at the dermal-epidermal interface provides evidence of this recognition. The lichenoid reaction is confined within that domain whose boundary is the peripheral interface between the clonal epidermal component and the adjacent more normal epidermis. The lichenoid reaction may be represented in primary, established, or senescent patterns; often the patterns are mixed as they are in lichenoid keratoses.

In this field, the epidermis shows hyperkeratosis, a prominent granular layer, acanthosis, irregular erosions of the rete ridges, and liquefaction degeneration at the dermal-epidermal interface. The papillary dermis is widened and fibrotic; it contains band-like infiltrates of lymphoid cells. The patterns are clearly lichenoid (i.e., cell-rich, lichen planus-like type lichenoid reaction).



S13C14P12-2: To the left, the epidermis is hyperplastic, but a basal layer and a basal unit are preserved. The granular layer is hyperplastic; there is hyperkeratosis. To the right, a basal layer is not regularly recognizable and the basal unit is irregularly interrupted; the patterns are lichenoid. In the area of the lichenoid reaction, there are spotty areas of liquefaction degeneration at the dermal-epidermal interface. In this same region to the right, keratinocytes of the superficial unit are pale and individually hypertrophied (a pattern promoting terminal differentiation). At the interface between the two populations of keratinocytes, an angulated indentation has formed. A column of keratotic and parakeratotic debris projects from the surface of this indentation; this column is the cornoid lamella of porokeratosis. Beneath the indentation, the granular layer is interrupted. There is nuclear disarray in the population of keratinocytes beneath the column; many of the keratinocytes show perinuclear vacuoles. The dermis shows fibrosis and telangiectasia. To the right, the vacuoles and defects at the dermal-epidermal interface are combined in a pattern that is lichen planus-like.

S13C14P12-3: In this area of a lesion of porokeratosis, lichenoid patterns are represented at the dermal-epidermal interface. Lymphocytes and migratory histiocytes are loosely sprinkled in the dermis near the basement membrane. There are lytic defects in the basal layer of the epidermis; the defects contain lymphocytes, histiocytes, and necrotic keratinocytes. Similar lytic defects are present in the epidermis near the interface between the basal and the superficial units. There is a prominent necrotic keratinocyte, in the same general area, near the top of the field.

S13C14P12-4: A well-developed lichenoid reaction of lichen planus-like type is represented in this field. Blue arrows identify reduplicated basement membrane. The central defect, containing colloid bodies, lymphocytes, and histiocytes, provides a marker for a portion of the epidermal domain that has been destroyed (the defect includes a portion of the basal unit of a rete ridge).

In this field, the lichenoid reaction has been caught in an act in which a portion of the epidermal domain will by a process of accretive fibrosis become an expansion of the dermal connective tissue. The act is a distinctive process of organization in which new fibrous tissue will be inlaid in the defect. Above the center of the field, the basal layer of the epidermis has undergone lysis. The overlying epidermis has the qualities of an hypertrophied superficial unit with hypertrophy of individual keratinoctes; the patterns are clearly lichen planus-like.

S13C14P12-5: As with most lichenoid reactions, the lichenoid process, in a lesion of porokeratosis, may be encountered in primary, established, or senescent patterns. In this example in this field, the pattern is that of a senescent lichenoid reaction. The epidermis shows hyperkeratosis, hypergranulosis, and acanthosis; rete patterns are effaced. The widened papillary dermis shows fibrosis and edema. Vessels are tortuous and increased in number; they are ectatic. There are mild perivascular infiltrates of lymphoid cells. A cornoid lamella is not represented in this field. The pattern is poikilodermatous.

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