[Acquired dermal melanocytosis: clinical, pathological and ultrastructural study]

Dermal melanocytosis is characterized by the presence of ectopic melanocytes in the dermis. There are several clinical forms. This report describes an unusual case of acquired dermal melanocytosis probably associated with leptomeningeal melanosis. An ultrastructural study was performed.

A 52-year-old Caucasian woman presented with a fifteen-year history of slowly spreading gray-blue macular pigmentation, associated with multiple blue nevi. Histologic examination revealed dermal melanocytosis. An extracellular sheath surrounded the melanocyte and their cytoplasmic processes. Medullar magnetic resonance findings were compatible with leptomeningeal melanosis.

Dermal melanocytosis is thought to represent a disorder of neural crest migration. Melanocytes are thought to be aberrant and become arrested during migration, remaining in the dermis. Reactivation of latent dermal melanocytes should explain the pathogenesis of acquired forms. Ultrastructural examinations show an extracellular sheath enclosing dermal melanocytes in all types of dermal melanocytosis.