S3C13P2-Lichen Striatus

S3C13P2-1: With lichen striatus as a model, the lichenoid reaction can be divided into stages. In the first stage, the primary pattern (left) is psoriasiform with hyperplasia of the basal unit and elongation of rete ridges. Lymphocytes infiltrate the epidermis among keratinocytes of the basal unit . In the established (second) phase (center), the reaction is lichen planus-like with lytic defects involving both the basal layer and the basal unit. The superficial unit of the epidermis is hyperplastic. The late stage (right) qualifies as a senescent lichenoid reaction. The interface between the epidermis and the dermis is relatively straight and there is a reduction in the density of the inflammatory infiltrates.

S3C13P2-2: The cells of the basal unit of the epidermis have their long axes arranged perpendicular to the plane of the surface of the skin. These cells are smaller than cells of the superficial unit; they tend to have cytoplasm that is more basophilic than acidophilic. Hyperplasia of the basal unit results in a psoriasiform pattern with elongation of the rete ridges. Hyperplasia of the basal unit often results in the formation of a zone of parakeratosis at the surface. Cells of the superficial unit are polygonal and have their long axes parallel to the plane of the surface of the skin. They have acidophilic cytoplasm with prominent tonofibrils. Hyperplasia of the superficial unit is likely to be associated with compact hyperkeratosis and a prominent granular layer. Basically, a process, which erodes the basal unit and produces hyperplasia of the superficial unit, is likely to be interpreted as lichen planus. In practice, such a pattern may be a basic response to a form of injury without great etiologic specificity; the category of lichen planus may not be representative of a single, specific disorder.

S3C13P2-3a&b: The full expression of the epithelial involvement in lesions of lichen striatus is seen in S3C13P2-3a (to the left). There are lytic defects along the dermal-epidermal interface that are associated with band-like infiltrates of lymphoid cells (the patterns in this area are mostly established). Blue arrows identify a follicular component (see S3C13P2-3b). Lymphoid cells in the pattern of a “swarm of bees” surround and have invaded the follicle. Lytic defects are not prominent (the pattern has primary qualities). Red arrows identify an involved sweat gland, again in the patterns of a swarm of bees (lymphoepithelial lesion).

S3C13P2-4: In this area, the follicular epithelium shows hyperplasia of the “superficial” unit and hyperkeratosis (the lumen is dilated). Focally, there are lytic defects in the basal unit of the follicular epithelium (established lichenoid pattern).

S3C13P2-5 & 6: In fig.5 on the left at the dermal-epidermal interface, the lichenoid changes are advanced; a basal unit cannot be defined morphologically. Red arrows point to a follicular pattern that also has established qualities. Blue arrows point to a pattern that has senescent qualities. Green arrows identify established and senescent patterns at the dermal-epidermal interface (lichen striatus; the patterns would also be in keeping with a diagnosis of lichen planopilaris). In S3C13P2-6, there are prominent mucinous changes in the perifollicular sheath in association with the band-like infiltrates. In addition, the hyperplastic basal unit of the follicular epithelium shows mucinosis (the mucinous interstitium is expanded; with this colloidal iron stain the mucinous material is green).

S3C13P2-7: The effects of the lichenoid reaction on the sweat gland apparatus is immunostimulatory. The epithelium shows crowding of the nuclei of the epithelial cells with enlargement and hyperchromatism of scattered nuclei. The lymphoid infiltrates in the adventitia contain plasma cells. In some examples, the lymphoid cells migrate into the epithelium to produce a variation of a lymphoepithelial island.

S3C13P2-8: In this area, the epithelium of the affected sweat glands is hyperplastic; lymphoid cells intermingle among the epithelial cells. In some areas, the epithelial islands are solid; lumina have been obliterated in the solid areas. The combined patterns qualify as lymphoepithelial islands; the changes are comparable to those of the lymphoepithelial islands of Sjogren’s syndrome.

 

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