Actinic reticuloid.
AR can be regarded as the most severe variant of the spectrum of chronic actinic dermatitis. The exact etiology is still unknown, but is probably multifactorial, involving contact allergic, photoallergenic, phototoxic, immunologic, and metabolic factors. A diagnosis of AR should only be made when the following criteria are present: (1) persistent infiltrated papules and plaques on light-exposed skin, often with extension to covered areas or generalized infiltrated erythroderma; (2) photosensitivity to a broad spectrum of wavelengths, including UV-B, UV-A, and part of the visible spectrum; and (3) on histologic examination, a dermal infiltrate with presence of atypical lymphoid cells. When one or two criteria are lacking, the more general term chronic actinic dermatitis should be preferred. The presence of a lymphoid infiltrate dominated by CD8+ cells seems to be useful as an additional marker for a diagnosis of AR. A CD8+ predominance in dermal infiltrates is exceptional and has been reported in clinically distinguished conditions such as graft-versus-host disease, lichen planus, erythema multiforme, and pityriasis lichenoides acuta, as well as chronica, and, finally, in mycosis fungoides. In erythrodermic patients, the presence of a CD8+ -dominated dermal infiltrate and, especially, a reversed CD4+ to CD8+ ratio in the peripheral blood are highly characteristic for a definite diagnosis of AR. It is not known why preferentially CD8+ lymphocytes occur in AR. Exposure to UV radiation can induce the presence of suppressor cells. In late lesions of polymorphic light eruption, there is also an increase of CD8+ cells as compared with early lesions, perhaps contributing to local suppression of the inflammatory response.(ABSTRACT TRUNCATED AT 250 WORDS)