S3C16P5-2: The patterns are lichenoid at the dermal-epidermal interface; they are lichenoid in respect to the lysis of the basal unit of the epidermis.The band-like infiltrates identify the process as a cell-rich variant. The infiltrates fill the papillary dermis. They extend along vessels into the reticular dermis. There is hyperkeratosis and papillomatosis. The follicle to the right of the center of the field shows changes similar to those of lichen plano-pilaris. These follicular changes are compatible with progression in the follicular lymphoepithelial lesion of lichen striatus; they are acceptable as a variation in the setting of lichen striatus. They are representative of a stage in the evolution of follicular mucinosis, but the follicular changes clearly are secondary.

S3C16P5-5: The immunoproliferative phase of secondary follicular mucinosis, in this lesion of lichen striatus, is characterized by an increased number of nuclei per unit area. This in part is due to an increase in small, somewhat spindle shaped, keratinocytes (i.e., dedifferentiation of follicular epithelial cells) and to an infiltrate of small lymphocytes among the keratinocytes. The pattern is representative of a primary lichenoid reaction. It might be additionally characterized as having pityriasic qualities. It also qualifies as a variant of a lymphoepithelial lesion.

S3C16P5-6: This lichenoid reaction is focal and rather cell-poor. It has eroded the basal unit in the region of the arrows. In the same area, the superficial unit is hyperplastic (i.e., increased prominence of cells showing terminal differentiation). The changes in the keratin layer are mild.

S3C16P5-7: The lichenoid reaction is spotty and established. There is focal parakeratosis. The basal unit is eroded. The lesion has a “nitidus” quality (lichen striatus).

S3C16P5-8: This primary pattern is psoriasiform and spongiotic. Without clinical information and/or representation of adnexal components, the patterns could be easily dismissed as a psoriasiform dermatitis. Focally, the patterns also are acceptable as those of a primary lichenoid reaction (lichen striatus). The patterns, in combination, qualify as pityriasic.

S3C16P5-9: The epidermal, follicular, and sweat glandular lymphoepithelial changes of lichen striatus are represented. The epidermal and the follicular changes are usually dismissed as lichenoid reactions, but the epidermal changes also could be characterized as a cytolytic lymphoepithelial lesion. The follicular changes could also be accommodated in the spectrum of follicular mucinosis. The sweat gland changes are usually characterized as a lymphoepithelial lesion, but also could be characterized as a primary lichenoid reaction. These characterizations are conveniences for dermatopathologists, but tend to lend specificity to what is a basic reaction between T lymphocytes and target cells. In addition, the effects of the interactions are expressed as stages, some of which, by the nature of the associated products, are given specific designations, as if they are specific diseases (i.e., follicular mucinosis).

S3C16P5-10: This component of a lesion of lichen striatus could be easily accommodated in the category of lichen plano-pilaris, or even keratosis pilaris. The pattern is representative of the established phase of a follicular lichenoid reaction; it is independent of pigeon-holes commonly favored by dermatopathologists, who see patterns chiseled in stone. In such an approach, there is no appreciation for the evolving character of biologic processes. The follicular component is a cytolytic, lymphoepithelial lesion showing partial survivial of a follicular superficial unit and an overproduction of compact keratin (a marker for an excessive shift in the rate, and degree, of terminal differentiation).