Histopathological features of acquired dermal melanocytosis

Acquired dermal melanocytosis (ADM) is the term used for pigmentary disorders characterized by blue brown macules, most frequently seen on the face (acquired bilateral nevus of Ota-like macules, ABNOM), and rarely found on the trunk or extremities. Although extrafacial ADM and ABNOM are not usually considered separate entities because of similar features, there has been debate as to whether extrafacial ADM and ABNOM might be part of the same disease spectrum, with or without the same pathogenesis. In order to investigate the relationship between these two entities, the histopathological features of extrafacial ADM and ABNOM were evaluated. We examined nine cases of extrafacial ADM and ten cases of ABNOM. Biopsies were performed on both normal and lesional skin, or on lesional skin only. The sections were stained using hematoxylin-eosin, Fontana-Masson, and NKI/beteb. There was no difference in the degree of melanin pigmentation and the number of melanocytes per unit area in the lesional skin of the epidermis and dermis in the comparisons between extrafacial ADM and ABNOM. The mean depth of the dermal melanocytes was significantly increased in extrafacial ADM (0.88 +/- 0.19 mm) compared to ABNOM (0.58 +/- 0.19 mm); however, in both extrafacial ADM and ABNOM, dermal melanocytes were distributed from the upper to the mid dermis. In conclusion, there was no significant difference in the histopathological features, including relative depth of melanocytes, between extrafacial ADM and ABNOM. To the best of our knowledge, this is the first study to demonstrate by histopathology that extrafacial ADM is the same as ABNOM.