The spectrum of benign dermal dendritic melanocytic proliferations

Dermal melanocytoses (DMs) comprise a heterogeneous group of benign lesions, located on skin and mucous membranes, characterized by dendritic melanocytes in the dermis. Although they share common histopathological features, some variants may present only as bluish or grey patches, some only as papules/nodules/plaques and others may show combination of all of these lesions. Despite the fact that blue naevus (BN) is typically characterized with papulonodular lesions, its variants may show all of the aforementioned presentations. Mongolian spot, naevus of Ota and naevus of Ito are patchy DMs distinguished by their specific localizations. Apart from these classical forms, many atypical variants without unique clinicopathological characteristics have been described in the literature making the nomenclature of DMs more complicated. However, congenital dermal melanocytosis and acquired dermal melanocytosis seem to be crucial umbrella terms that encompass all patchy DMs in atypical locations. Papules or subcutaneous nodules on patchy lesions and association of epidermal pigmentation presenting as brownish patches may be encountered as rare features of DMs. On the other hand, delayed-onset subcutaneous nodules may be typical presentations of melanoma in patchy DMs; therefore, they deserve special attention. Large plaque-type BN with subcutaneous cellular nodules is a newly described entity, harbouring clinical features of various DMs together and has a high risk of melanoma. The whole spectrum of dermal dendritic melanocytic proliferations is discussed including novelties and controversial issues.