Acquired dermal melanocytosis (ADM) is a rare, benign pigmentary disorder characterized by dark gray or brown macules and patches, most commonly on the face (also known as Hori nevus and acquired bilateral nevus of Ota-like macules). Other uncommon locations that have been reported include the extremities, back, and trunk.

Onset of facial lesions is usually in late adolescence or early adulthood. Patients with extrafacial ADM have a variable age of onset of pigmentation. While the majority of facial cases occur in female patients of East Asian origin, extrafacial presentation has a more varied sex and ethnic distribution. Patients usually have darker skin phototypes (Fitzpatrick skin phototype III or greater).

The etiology and pathogenesis of ADM is unclear. It is believed that immature dermal melanocytes may be activated by a trigger such as ultraviolet radiation, chronic inflammation, chemical exposure, or excessive sex hormones (ie, estrogen).

Related topic: congenital dermal melanocytosis