Becker naevus
Becker's melanosis; pigmented hairy epidermal nevus; "Becker melanosis"; (in extensive form, Becker's naevus syndrome)
The Becker naevus โ first described by SW Becker in 1949 โ is a common acquired or rarely congenital cutaneous hamartoma, classically presenting in adolescence as a unilateral, well-demarcated, irregularly bordered, brown hyperpigmented patch (5โ20 cm) on the shoulder, scapula or upper anterior chest of a young man, with progressive development of overlying terminal hypertrichosis from puberty onwards. Recent molecular work has demonstrated postzygotic somatic mosaic activating mutations of ACTB (ฮฒ-actin) โ placing Becker naevus among the postzygotic somatic mosaic disorders alongside naevus sebaceus (HRAS/KRAS) and naevus spilus (HRAS). Becker naevus is benign with no documented malignant potential of clinical significance โ but the clinical entity often presents diagnostic confusion with congenital melanocytic naevus, cafรฉ-au-lait macule (NF1) and segmental hyperpigmentation. Becker's naevus syndrome is a rare extended phenotype with ipsilateral hypoplasia of breast, pectoralis muscle or limb, scoliosis or other skeletal anomalies.
Clinical features
- Unilateral, well-demarcated, irregularly bordered, brown to tan hyperpigmented patch.
- Size 5โ20 cm; occasionally smaller or much larger.
- Distribution โ shoulder, scapula, upper anterior chest, deltoid; less often face, lower back, abdomen, lower limb.
- Onset typically in adolescence (10โ20 years); occasionally congenital.
- M:F ~5:1; cosmetic concern is the principal presenting issue.
- Hypertrichosis โ terminal hairs develop within the lesion from puberty (testosterone-driven); often the most cosmetically intrusive feature for boys.
- Surface texture โ slightly rough; occasional acne-like papules within the lesion (driven by sebaceous gland hyperplasia within the affected area).
- Becker's naevus syndrome โ extensive Becker's naevus + ipsilateral hypoplasia of breast tissue, pectoralis major / pectoralis minor, scoliosis, accessory cervical ribs, leg-length discrepancy or other skeletal anomalies.
Genetics & pathogenesis
- Postzygotic somatic mosaic gain-of-function mutations of ACTB (ฮฒ-actin) โ ~70% of cases tested.
- Confined to the affected lesion.
- Driver of the increased local androgen receptor expression that produces the hypertrichosis and acneiform features.
- Joins naevus sebaceus (HRAS / KRAS), naevus spilus (HRAS) and Schimmelpenning syndrome (HRAS) in the spectrum of postzygotic somatic mosaic skin hamartomas.
Histology
- Epidermal hyperpigmentation with mild acanthosis.
- Increased basal-layer melanin; melanocyte numbers normal or only mildly increased.
- Smooth-muscle hyperplasia (arrector pili) โ characteristic and diagnostic.
- Increased sebaceous and apocrine glands.
- Increased pilosebaceous units accounting for the hypertrichosis.
- No atypia.
Cancer risk
- Becker naevus is benign with no documented melanoma risk above background.
- Rare reports of melanoma arising within Becker naevus exist but are no more frequent than melanoma in similar areas of unaffected skin โ most experts consider any apparent association coincidental.
- Surveillance is therefore not specifically indicated for cancer; however, reassurance and routine skin surveillance per the patient's overall melanoma risk are appropriate.
Management
- Reassurance โ Becker naevus is benign and stable in adulthood; no cancer surveillance indicated.
- Cosmetic management of pigmentation:
- Q-switched lasers (Nd:YAG 1064 nm, ruby 694 nm, alexandrite 755 nm) โ variable response; multiple sessions; risk of post-inflammatory hyperpigmentation.
- Picosecond lasers โ emerging.
- Topical depigmenting agents โ limited efficacy.
- Camouflage cosmetics.
- Cosmetic management of hypertrichosis:
- Long-pulsed alexandrite 755 nm or diode 810 nm laser hair reduction โ first-line; multiple sessions.
- Electrolysis for finer control.
- Topical eflornithine (limited).
- Becker's naevus syndrome โ orthopaedic, plastic / breast surgery and physiotherapy MDT for the structural anomalies; corrective surgery as appropriate.
- Genetic counselling โ somatic mosaic; not heritable; recurrence risk negligible.
References
- Becker SW. Concurrent melanosis and hypertrichosis in a distribution of nevus unius lateris. Arch Dermatol Syphilol; 1949.
- Cai ED et al. Postzygotic mutations in beta-actin are associated with Becker's nevus and Becker's nevus syndrome. J Invest Dermatol; 2017.
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