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LP-like VARIANTS (tier 2)
Annular lichen planus: When lesions of lichen planus spread centrifugally and resolve centrally, the patterns qualify as annular. If the central portion becomes atrophic, the lesion qualifies as “atrophic
lichen planus.”
In atrophic lichen planus, severe attrition of keratinocytes at the dermal-epidermal interface results in a thin, atrophic epidermis. Often, the dermal infiltrate is sparse. Laminated fibrous tissue, melanophages,
and an increased number of vessels are markers for the effects of an earlier established phase. Atrophic lichen planus qualifies as a senescent lichenoid reaction. Atrophic lichen planus may be difficult to
distinguish from a senescent lesion of the parapsoriasis-poikiloderma complex - a lesion that is also commonly expressed, early on, in cell-rich lichenoid patterns.
Lichen planus
is common on mucous membranes, although it is rare for lesion of lichen planus to be restricted to oral or genital mucosae (squamous mucosae). The basic histologic features seen in the cutaneous lesions are represented in the mucosal lesions. Focal parakeratosis is more common on mucous membranes than on skin. The granular layer may be poorly developed. Complete effacement of rete ridges is relatively common. Plasma cells may be represented in the infiltrations of mucous membranes; they are rarely a feature of cutaneous lesions with the exception of the hypertrophic variants. The mucous membrane lesions often demonstrate a remarkable chronicity and may be complicated by squamous cell carcinomas.
The nail matrix may be affected by lichen planus. The result is a distorted nail plate, or permanent loss of the afflicted nail. Atrophy is the occasional effect of lichen planus on cutaneous appendages (nails or
pilosebaceous units). Lesions of lichen planus on the palms and soles are occasionally ulcerated. Some of the reported cases may be examples of “mixed” lichenoid dermatitis (LP-LE overlap syndrome).
“Lichen plan folliculaire tumidus retro-auriculaire” is described as a variant in which the lesion clinically is tumoral and histologically displays a prominent, established follicular, lichenoid reaction (21).
Differential diagnosis:
The histologic definition of lichen planus does not define an etiologically homogeneous group of disorders. The idiopathic category is clinically varied as to distribution, number and size of lesions, and duration of
disease. This group is difficult to distinguish histologically from the reactions in some inflamed tattoos (22), from drug induced variants, or from
lesions induced by contact with a sensitizer (24). A prominent perivascular arrangement of lymphocytes in the reticular dermis, the presence of eosinophils,
and
variable, or incompletely developed, epidermal changes are more characteristic of the drug induced variants. A history of receiving gold, or some drug, such as quinacrine, is also helpful in the diagnosis of a drug related variant.
Since the reaction in lichen planus appears to be a T cell response, it is reasonable to expect an overlap of histologic features with other recognized T cell processes. The T cell dysplasias (10) are chronic, cutaneous disorders in which T cells are locally persistent and numerically and cytologically abnormal. They are additionally characterized
by a variable potential for progression to a T cell lymphoma (most observers group the dysplasias and the tumoral forms in the category of cutaneous T cell lymphoma [CTCL]). The concepts of T cell dysplasias embrace
pre-tumoral stages of the clinical syndromes of mycosis fungoides, the parapsoriasis-poikiloderma complex, and some of the evolving stages in the Sezary syndrome. The histologic overlap between the T cell dysplasias
and lichen planus are remarkable. Especially in the parapsoriasis-poikiloderma complex in which the cytologic dysplasia is mild, the life history of an individual lesion shares remarkable similarities with the life
history of a lesion of lichen planus. The lesions in the parapsoriasis-poikiloderma complex evolve from a cellular phase in which a band-like infiltration hugs the epidermis and produces attrition of the basal unit
to a cell-poor phase in which the epidermis is atrophic and a widened fibrotic papillary dermis contains ectatic blood vessels. The cell-rich phase of a progressive T-cell dysplasia shares features with the
established lichenoid reaction; the cell-poor phase (poikilodermatous phase) of a low grade, progressive T-cell dysplasia is prototypic of a senescent lichenoid reaction.
In the T cell dysplasias, the epidermis should be carefully examined for atypical lymphoid cells which have convoluted nuclei (prune-shaped nuclei) and uniformly dense chromatin. In distinguishing between a
dysplastic and a reactive, transformed T lymphocyte, the nucleus of the dysplastic cell is usually as large as the nuclei of neighboring keratinocytes. Unfortunately, there are dysplasias in which the cells are
characterized by small convoluted nuclei. In the more significant dysplasias, the numerical representation of dysplastic T lymphocytes in both the epidermis and dermis facilitates the diagnosis, but confidence is
sometimes compromised by small cell variants of progressive T cell dysplasias. Something more than the bombast of a papal dictate is required
In the dysplasias, the surviving superficial epidermal unit rarely shows hypertrophy of individual keratinocytes or the abnormal keratinized product of a typical lesion of lichen planus.
Non-lichen Planus-like Variants
The basic features of the lichenoid reaction, exclusive of those of lichen planus-like type, can be extended to provide for the interpretation of other, somewhat related reaction patterns of the skin. In several
disorders, a variation of a lichenoid reaction at the dermal-epidermal interface is combined with the pattern of a lymphocytic vasculitis. Lymphocytic vasculitides are characterized by uniform cuffs of lymphocytes
in the perivenular spaces of the reticular dermis. The involved vessels usually show thickened walls and endothelial swelling (25). Often clusters of
extravasated erythrocytes are found in the upper portion of the dermis. The pattern of lichenoid lymphocytic vasculitis
is basic to the reaction patterns in erythema multiforme, pityriasis lichenoides, and some lichenoid drug eruptions. It is seen in other processes, such as secondary lues.
In secondary lues, the infiltrations in the perivenular spaces and the papillary dermis often contain admixtures of plasma cells and numerous pale, migratory histiocytes. Occasionally, the histiocytes form
epithelioid aggregates. The patterns in the epidermis have lichenoid qualities. The response in the epidermis in lesions of secondary lues usually is either psoriasiform (as in a primary lichenoid reaction), erosive
along the dermal-epidermal interface (as in an established lichenoid reaction), or senescent (as in a senescent lichenoid response). Often psoriasiform and lichenoid qualities are combined; the combination has
pityriasic qualities. Lesions of secondary lues have a life history which, in toto, reflects the evolution of the lichenoid reactions. In lesions of condyloma lata, the epidermal response is psoriasiform and,
focally, has the qualities of spongioform pustules.
Another example of a lichenoid lymphocytic vasculitis is pityriasis lichenoides (25). In this variant, vessels in the reticular dermis are surrounded
by lymphocytes; they have thickened walls and swollen endothelium. The lymphoid infiltrates diffusely involve the papillary dermis; they migrate into the epidermis. They characteristically contain clusters of
extravasated erythrocytes. The epidermal changes are distinctive. The keratin layer is usually parakeratotic and, often, contains neutrophils. The superficial unit is poorly developed. The individual keratinocytes
of the superficial unit are small; they show cytoplasmic pallor. Interstitial spaces in the atrophic, superficial unit are widened and, in some examples, contain infiltrates of lymphocytes. The basal unit of the
epidermis often is hyperplastic with marked accentuation of the interstitial spaces. The individual basal keratinocytes often have distinctive, basophilic cytoplasm (a feature of regenerating cells). Lytic defects
are common in the basal unit. They contain lymphocytes and coagulated keratinocytes. For some examples, some of the lymphocytes in the dermal and epidermal infiltrates will have the nuclear characteristics of
transformed T lymphocytes. The infiltrates often involve skin appendages, particularly sweat ducts. The reaction in the epidermis and the papillary dermis in lesions of pityriasis lichenoides usually qualifies
as a primary lichenoid response; it has pityriasic qualities. The total response is that of a lichenoid lymphocytic vasculitis. The reaction in pityriasis lichenoides may be an additional expression of cell-mediated
immunity in which the antigenic determinants are different from those in the lichen planus-like category. Rarely, the superficial unit of the epidermis in a lesion of pityriasis lichenoides is hyperplastic, as
in a lesion of lichen planus. Patterns in pityriasis lichenoides may also overlap with those of erythema multiforme.
Lymphomatoid papulosis shares histologic and clinical features with pityriasis lichenoides (26). In occasional lesions, a distinction between the two
disorders is difficult. Some of the lymphoid cells in both disorders have the characteristics of dysplastic T lymphocytes. Wilson-Jones, et al (26), in
defining criteria, that might aid in distinguishing pityriasis lichenoides from lymphomatoid papulosis, evaluated the percentage of dysplastic T lymphocytes. He assigned those cases in which the ration of atypical
lymphocytes was 10%, or greater, to the category of lymphomatoid papulosis. This approach has apparently fallen out of favor; many observers consider the two processes to be unrelated. On the other hand, there seem
to be examples of pityriasis lichenoides in which a high component of transformed T lymphocytes is a feature. In addition, some cases modulate in regard to the histologic character of individual lesions. In such
examples, patterns, at times, resemble lymphoma; at other times, they resemble lymphomatoid papulosis; and at still other times, they resemble pityriasis lichenoides. The relationships are unclear. Some examples of
lymphomatoid papulosis involve into peculiar immunoblastic lymphoma-like lesions which may also display the quality of self-healing (large cell “lymphomas” that are CD30+). These lymphoproliferative lesions often
are pleomorphic and contain numerous large blast cells, some of which are multinucleated. Lesions of this type may also be de novo. Some examples are included in some reports of primary cutaneous Hodgkin's disease (27).
Erythema multiforme
is basically a lichenoid lymphocytic vasculitis. It is characterized by perivascular, lymphoid infiltrates in the upper reticulardermis and the papillary dermis. The infiltrates concentrate in the basal layer of the epidermis; they produce focal lytic clefts, or a subepidermal vesicle (23). Within the clefts, lymphocytes intermingle with loosely clustered, coagulated keratinocytes. The cells in the surviving basal unit rapidly regenerate
around the inflammatory and necrotic debris (i.e., necrotic keratinocytes). The necrotic keratinocytes are compacted within the whorls of regenerating keratinocytes. They are carried to the surface of the skin in
concert with the regenerating cells (pattern of whorled transepidermal elimination). This pattern is characteristic, but not diagnostic: it nay be seen in the roof of subepidermal vesicles, as in lesions of bullous
pemphigoid. The keratin layer is usually unaffected in the early stages of this histologically characteristic reaction (28).
Changes basically similar to erythema multiforme occur in some examples of fixed drug eruption and in toxic epidermal necrolysis. In the lichenoid fixed drug reaction, a marked melanoderma and lamellar
fibrosis in a widened papillary dermis are markers for a "fixed" or repetitive insult. In addition, the keratin layer may be abnormal in contrast to the usual pattern in a lesion of erythema multiforme.
The inactive phase of a fixed drug reaction qualifies as a senescent lichenoid reaction (28).
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