The term lymphomatoid contact dermatitis was coined by Gomez Orbaneja etal.  in 1976. These authors described four patients with persistent allergic contact dermatitis proved by patch tests. The clinical picture and histological features in their patients were highly suggestive of mycosis fungoides. Clinically, lymphomatoid contact dermatitis is characterized by pruritic erythematous plaques (Fig. 20.3). Generalized plaques or exfoliative erythroderma can be observed rarely. The lesions undergo phases of exacerbation and remission.
Histologically, lymphomatoid contact dermatitis resembles mycosis fungoides (Fig. 20.4) . The differentiation is performed mainly on the basis of changes within the epidermis. In lymphomatoid contact dermatitis, there are usually only a few intraepidermal atypical lymphocytes that have no tendency to form 'Darier's nests' ('Pautrier's microabscesses'). Small intraepidermal collections of keratinocytes admixed with Langerhans cells and a few lymphocytes are common, and should not be misinterpreted as true 'Darier's nests' (Fig. 20.5). Staining for CD1a highlights Langerhans cells in these intraepidermal collections (Fig. 20.6). Analysis
of TCR gene rearrangement commonly shows a polyclonal population of T lymphocytes in the skin lesions of lymphomatoid contact dermatitis. However, in the majority of patch test lesions in patients with 'conventional' contact dermatitis, monoclonality can be observed by Southern blotting, demonstrating that the finding of a clonal population of T lymphocytes in such patients does not have any diagnostic implications .
Patch tests to a variety of common antigens can give a positive reaction in lymphomatoid contact dermatitis and the
diagnosis should be reserved for patients in whom the lymphomatoid skin lesions are caused by a positively reacting antigen. Although lymphomatoid contact dermatitis has been reported to evolve into true malignant lymphoma, it is more likely that such patients had malignant lymphoma from the outset. For the management of patients, a thorough search for antigens is necessary in order to interrupt the process. When contact with the responsible allergens is avoided, the lesions heal in a relatively short time.
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