Acne arising on a facial Becker nevus following the lines of Blaschko*

Dear Editor, Becker nevus (BN) is characterized by a unilateral lesion consisting of hypermelanosis and hypertrichosis. It develops on the upper torso, shoulders, or arms, especially of male adolescents. Most cases are acquired, and the time of onset varies from infancy to adulthood. Although the etiology of this nevus is not yet known, an association with the expression of androgen receptors is proposed.1 Due to an unusual presentation, we report the case of a young adult patient with acne arising on a facial BN following the lines of Blaschko. A 28-year-old male patient complained of a linear, hyperpigmented lesion on the forehead and nose since the age of 15 years. Three years after the onset, the patient repeatedly presented with pustules and nodules only on the right side of the nose, which led to the development of a scar area on the site. Physical examination revealed a linear, hyperpigmented, and brownish macula on the forehead and right side of the nose, with dark terminal hairs. We also observed a scarring area on the same side of the nose, completely sparing the left side and the right nasal wing (Figure 1). Interestingly, the macula closely followed one of the lines of Blaschko on the face (Figure 2). A histopathological study revealed acanthosis and hyperpigmentation of the basal layer in the epidermis (Figure 3). In some areas, the dermis showed smooth muscle hyperplasia, confirming the diagnosis of BN (Figure 3). BN is a cutaneous hamartoma characterized by a generally large hyperpigmented and unilateral area, with irregular borders and dark terminal hairs in about 50% of cases. Although the sites of predilection are shoulders, anterior aspect of the thorax, and scapular region, any other area of the body can be affected. Anatomopathological examinations of BN reveal alterations of the epidermis characterized by acanthosis with regular lengthening of interpapillary ridges. In some cases, papillomatosis is also found. Hyperpigmentation of basal layer cells are observed, and melanophages can be found in the papillary dermis. The number and size of piloerector muscles are increased, often resulting in an indistinguishable aspect from smooth muscle hamartoma (SMH). Acne rarely appears in a segmental manner, usually occurring in cases of mosaicism such as nevus comedonicus, Happle-Tinschert syndrome, and Alpert syndrome. It is also usually associated with epidermal nevi, such as BN. A review of 375 cases demonstrated that most patients (n = 349) were affected by nevus comedonicus, all following the lines of Blaschko.2 In relation to the association with BN, only 10 cases were described, all in the thoracic region with a block-like configuration, none of them following the lines of Blaschko.2 The first description of acne in a BN patient was reported in 740