A 12-year-old boy presented with a gradually progressive asymptomatic area of discoloration over right forearm since last 2 years. Examination revealed a unilateral, well-circumscribed 6cm x 8cm tan-brown patch on the right forearm, and having irregular border and blotchy pigmentation at the periphery (Fig. 1). Localized coarse hair and acneiform eruptions were observed, restricted to the patch. Darier sign was negative. No skeletal, soft tissue or neurological abnormalities were found on further examination. A diagnosis of Becker melanosis was made and the benign nature of the condition explained to the family.

Fig. 1 Well-circumscribed tan-brown patch on the forearm, having irregular border and blotchy pigmentation at the periphery with localized coarse hair and acneiform eruption.

Becker melanosis is typically characterized by unilateral circumscribed hyperpigmentation that usually begins at puberty and displays features of androgen sensitivity like hypertrichosis, and acneiform eruptions. Several skeletal or soft tissue anomalies can be associated with Becker melanosis (Becker nevus syndrome). The common mimickers of the condition are melanocytic nevus (usually congenital, lacks acneiform eruption), café au lait macules (present since birth, no hypertrichosis), and plexiform neurofibroma (‘bag of worms’ sign, presence of other features of neurofibromatosis). Topical flutamide or Q-switched ruby or Er: YAG laser can be used to treat the cosmetic concerns regarding the condition.