Chronic actinic dermatitis/actinic reticuloid: a clinicopathologic and immunohistochemical analysis of 37 cases.

Chronic actinic dermatitis/actinic reticuloid (CAD/AR) is an eczematous hypersensitivity reaction to ultraviolet rays that can vary from mild eczematous cases to AR, the most severe cases which may resemble cutaneous T-cell lymphoma. Diagnosis is based on clinical, histopathologic, and photobiologic features. In this study, we characterize the histopathologic and immunohistochemical features of 40 biopsies from 37 patients with established CAD. The cohort included 30 men and 7 women, ranging in age from 38 to 84 years (median, 62 years) and with a median duration of symptoms at presentation of 3 years (range, 1 to 40 years). All patients presented with erythematous lichenified plaques on sun-exposed areas. Severe cases (12/37) had extension to non-exposed areas. Positive photo-testing (20/20) and patch-testing (10/10) results, and cases with a high peripheral blood eosinophila (7/24) and HIV positivity (4/37) were noted. Skin biopsies demonstrated eczematous features including parakeratosis, acanthosis, spongiosis, and prominent dermal fibroplasia. Dermal dendrocytes were prominent in all cases with frequent multinucleated giant cells positive for factor XIIIa and S100 protein. Most cases displayed a brisk lymphocytic infiltrate with subtle exocytosis, atypical lymphocytes, and increased numbers of Langerhans cells, eosinophils, and plasma cells. There was a predominance of CD8 T cells within the epidermis (20/25) and a low CD4:CD8 ratio was noted in 20 of 25 cases. T-cell clonality studies were negative in 10 of 10 cases. CAD/AR may be difficult to distinguish from eczematous variants of cutaneous T-cell lymphoma. Important clues to differentiate both conditions include the identification of prominent dermal dendrocytes with multinucleated giant cells, eosinophils, plasma cells, and a low CD4:CD8 ratio.