Nevus depigmentosus: Clinical features and histopathologic characteristicsin 67 patients

Background: Nevus depigmentosus is defined as a congenital nonprogressive h ypopigmented macule or patch that is stable in its relative size and distri bution throughout life. The pathogenesis and histopathologic characteristic s of nevus depigmentosus is not yet fully established. Objective: The purpose of this study was to investigate the clinical and hi stopathologic characteristics of nevus depigmentosus as well as its pathoge nesis. Methods: A clinical survey was done with 67 patients diagnosed as having ne vus depigmentosus. Two skin biopsy specimens each were taken from 18 patien ts: one from the central part of the depigmented lesion and another from th e border of the lesion, including perilesional normal skin. The sections we re stained with hematoxylin-eosin, Fontana-Masson, and S-100 protein. Ultra structural evaluation was also done to detect changes of the melanocytes. Results: The lesions were mostly present before 3 years of age (92.5%), but some lesions also appeared later in childhood (7.5%). The back and buttock s were the most commonly affected sites, followed by the chest and the abdo men, the face, the neck, and the arms. Forty patients (59.7%) had the isola ted type of nevus depigmentosus and 27 patients (40.3%) had the segmental t ype. Histopathologic studies showed that the staining ability of Fontana-Ma sson in nevus depigmentosus lesions decreased compared with perilesional no rmal skin. However, there were no changes in the numbers of melanocytes ide ntified as S-100-positive cells in the basal layer. Electronmicroscopic stu dies revealed a great reduction in the number of melanosomes in melanocytes and some membrane-bound aggregated melanosomes were observed in keratinocy tes. Conclusion: The results of this study support the hypothesis that nevus dep igmentosus is caused by the functional defects of melanocytes and the morph ologic abnormalities of melanosomes.