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Pityriasis Lichenoides Chronica (tier2)
The category of pityriasis lichenoides chronica (PLC) is poorly defined. The designation carries with it the implication that PLC
is a chronic phase of PLVA.
Childhood pityriasis lichenoides chronica seems to be a distinct process, independent of PLVA. The epidermal patterns are mildly
psoriasiform; some examples show some elongation of the rete ridges. The epidermis shows both basal and superficial unit hyperplasia. The dermal infiltrates are perivascular; focally, lymphoid cells migrate into the
epidermis. For some lesions, the epidermal patterns are spongiotic; the spongiotic vesicles of such lesions are rich in histiocytes. For other examples, the epidermal patterns may have lichenoid qualities with focal
lysis of keratinocytes and liquefaction degeneration at the dermal-epidermal junction. The infiltrates, however, are limited in distribution; they tend to extend into the epidermis at the tips of dermal
papillae (S4C21P13-1-5) (a spongiotic quality).
Lymphoid cells in both the epidermis and the dermis may show enlargement of nuclei and nuclear irregularities (convolutions). The
chromatin tends to be delicately distributed. The nuclear changes may be sufficient to warrant a characterization of the process as a mild T-cell dysplasia of indeterminate type (S4C21P13-6-7).
In the pictorials, S4C22P14-1-6, two cases of
childhood “CTCL” are documented. One patient was a 12 year old boy with a history of a generalized, mildly pruritic eruption for 2 years. There were scattered, hypopigmented macules with dry follicular scale on
abdomen, back, upper arms, legs, and face. There was no adenopathy, or organomegaly. The second example of childhood “CTCL” was a 9 year old male with a history of a hypopigmented eruption for one year. Lesions were
only occasionally pruritic. There were multiple, hypopigmented macules widely distributed over the patient’s body.
The epidermis shows hyperplasia of the superficial and basal units. The superficial unit shows hyperkeratosis with a prominent
granular layer. In areas, rete ridges are elongated. Band-like infiltrates of lymphoid cells fill the papillary dermis (S4C22P14-1-6). The
infiltrates hug the epidermis and have migrated into the basal unit. Lytic defects are present in the basal unit. Some of the keratinocytes adjacent to the defects show dyskeratotic changes. In the basal unit of the
epidermis, the lymphoid infiltrates are cell-rich; the richness of the infiltrates in the epidermis would be considered, by some observers, as sufficient to justify a classification of the lesions as cutaneous
T-cell lymphoma. In areas, rete ridges are partially eroded; they have pointed extremities. Nuclei of the lymphoid cells are small. In the epidermis, the nuclei tend to be irregular in outline.
The patterns are psoriasiform and lichenoid; they have pityriasic qualities. They are distinguished from PLC (pityriasis
lichenoides chronica) by the density and diffuseness of the infiltrates in the papillary dermis and by the richness of the epidermal lymphoid infiltrates. The nature of this disease is uncertain. Progression to a
true lymphoma seems to be uncommon and is a poorly documented event.
Crowley JJ, Varghese A, et al: Mycosis fungoides in young patients: Clinical characteristics and outcome. J Am Acad Dermatol 1998;
38: 696-701.
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