[Localized reticulate hyperpigmentation].

34 year-old pregnant woman presented with reticulate pigmentation of the flexures, the dorsum of the hands and the genitoperianal region. She was in good health and her family history was unremarkable. Histologic examination of the hyperpigmented patches revealed pigmented filiform downgrowths of the interfollicular epidermis and follicular infundibula, as well as small epithelial cysts. Upon immunohistochemical and ultrastructural studies, the number of melanocytes appeared normal. The elongated dendritic processes of the melanocytes contained many mature melanosomes. In the adjacent keratinocytes large melanosomes did not aggregate into complexes. The diagnosis of localized reticulate pigmentary disorder was established. The knowledge of the broad clinical spectrum of localized reticulate hyperpigmentations with its favorable prognosis is of practical importance. Genital or flexural pigmented lesions have to be differentiated from melanosis of the vulva or acanthosis nigricans. The presented case gives further evidence that many of the proposed entities characterized clinically by reticulate pigmented macules and hyperkeratotic follicular lesions are different phenotypic expressions of the same autosomal dominant genodermatosis.