Becker’s nevus
The history and physical exam are most consistent with Becker’s nevus, also known as Becker’s melanosis. This is a benign cutaneous hamartoma, usually found in males, characterized by a large, irregularly shaped brown patch, often with hypertrichosis.1 Becker’s nevus can be congenital but is more commonly noticed in late childhood or early adolescence, with thickening, increased pigmentation, and hair growth. Becker’s nevus is considered an overgrowth of epidermal pigment cells and hair follicles and is thought to be attributable to postzygotic mutations (with ACTB mutations most reported).1 It is often located unilaterally on the upper trunk but is occasionally present elsewhere on the body. Acne may occasionally develop within the nevus, which is believed to be triggered by puberty-associated androgens.1 The lesion tends to persist indefinitely but has no propensity for malignant transformation.
Jennifer Laborada
Becker’s nevus is generally an isolated skin lesion without other anomalies. However, in rare instances, it may be associated with ipsilateral breast hypoplasia or hypoplastic defects of the muscle, skin, or skeleton, which is known as Becker’s nevus syndrome.2 Treatment is not medically warranted for an isolated Becker’s nevus but may be pursued for cosmetic reasons. Although treatment is generally discouraged because of variable success, laser hair removal and laser therapy may be pursued to address the hypertrichosis and hyperpigmentation, respectively.
What is on the differential?
A café-au-lait macule (CALM) is a light- to dark-brown, oval lesion that commonly presents at birth or in early childhood. CALMs vary widely in size from less than 1.5 cm to more than 20 cm in diameter. They are asymptomatic and grow in proportion to the individual over time.3 Becker’s nevus can be distinguished from CALMs by the development of hypertrichosis, typical location and course, and other skin changes within the nevus.
Dr. Lawrence F. Eichenfield
Postinflammatory hyperpigmentation (PIH) is characterized by asymptomatic, darkened macules or patches that are brown to blue-gray in color. It is one of the most common causes of hyperpigmentation, particularly in skin of color, and can take months to years to resolve. PIH is caused by increased melanin production in response to a cutaneous inflammatory process, such as a drug reaction, allergy, mechanical or thermal injury, infection, phototoxicity, or an underlying skin condition.3 Our patient’s history with the lack of an inciting inflammatory process is more consistent with Becker’s nevus.
Erythema ab igne is a cutaneous reaction to heat that presents as a hyperpigmented patch with a reticular or mottled configuration and superficial venular telangiectasia. The lesion is initially erythematous and progresses to a pale pink to purplish dark-brown color.4 Causes include long-term use of a heating pad, laptop, electric blanket, or a hot water bottle. The absence of prolonged heat exposure in our patient’s history does not favor erythema ab igne.
Pigmentary mosaicism is characterized by a distinctive pattern of hyperpigmentation that follows the lines of ectodermal embryologic development, known as the lines of Blaschko.5 This condition is also known as linear and whorled nevoid hypermelanosis because of its streaky or swirl-like pattern. Pigmentary mosaicism can be present at birth or appear within the first few weeks of life. It is caused by genetic heterogeneity in neuroectodermal cells, which results in skin with areas of varying colors. Pigmentary mosaicism is unlikely in this case as our patient’s lesion does not follow the lines of Blaschko.
Ms. Laborada is a pediatric dermatology research associate in the division of pediatric and adolescent dermatology at the University of California, San Diego, and Rady Children’s Hospital, San Diego. Dr. Eichenfield is the vice chair of the department of dermatology and professor of dermatology and pediatrics at the University of California, San Diego, and Rady Children’s Hospital. Ms. Laborada and Dr. Eichenfield have no relevant financial disclosures.
References
1. Atzmony L et al. J Cutan Pathol. 2020;47(8):681-5.
2. Danarti R et al. J Am Acad Dermatol. 2004;51(6):965-9.
3. Paller A and Mancini AJ. “Hurwitz Clinical Pediatric Dermatology: A textbook of skin disorders of childhood and adolescence” 4th ed. Philadelphia: Elsevier Saunders, 2011.
4. Patel DP. JAMA Dermatol. 2017;153(7):685.
5. Kromann AB et al. Orphanet J Rare Dis. 2018;13(1):39.