Becker Melanosis

Background

Becker melanosis was described in 1948 by S. William Becker in two young men with acquired melanosis and hypertrichosis in a unilateral distribution.^[1] Since then, this condition has been termed Becker nevus.

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Pathophysiology

The pathogenesis and etiology of Becker nevus remain uncertain.

Androgens may play a role in Becker melanosis, as evidenced by its peripubertal development, male preponderance, hypertrichosis, occasional development of acneform lesions within the patch, and rare association with accessory scrotum in the genital region. In addition, a significant increase in the number of androgen receptors in Becker melanosis lesional skin has been reported.^[2]

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Epidemiology

Frequency

A study of 19,302 men aged 17-26 years revealed a prevalence of Becker melanosis of 0.52%.

Sex

Males are affected by Becker melanosis more often than females.

Age

Although Becker nevus usually is a sporadic condition that manifests in the peripubertal period, both congenital and familial cases^[3] have been described.

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Patient Education

Advise patients that Becker melanosis is a benign entity and does not require treatment except for cosmetic reasons.

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History

The earliest finding of Becker nevus is an asymptomatic irregular tan-to-brown patch, most commonly located over the shoulder, upper chest, or back, as shown in the image below.

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Becker nevus of chest wall with associated hypertrichosis. Courtesy of Jason K. Rivers, MD.

Pigmentation may be subtle, and onset most commonly occurs in the peripubertal period. The patch expands during the first several years as new irregular pigmented macules and patches develop at the periphery and coalesce with the larger patch. This expansion results in a geographic configuration that may cover a large area.

Several months to years after the appearance of pigmentation, thick brown-to-black hairs develop both within and in close proximity to the patch. Hair density is highly variable and occasionally, hypertrichosis does not occur.

The central area in the patch may thicken, and acne vulgaris may develop.

Once present, the patch remains indefinitely, although minimal pigmentary fading may occur in adulthood.

Occasionally, Becker nevus may be associated with smooth muscle hamartoma. Rarely, hypoplasia of underlying structures, such as unilateral breast hypoplasia, has been reported.^[4]

Other associations seen with Becker nevus include unilateral or ipsilateral pectoralis major aplasia, ipsilateral limb shortening, ipsilateral foot enlargement, spina bifida, scoliosis, pectus carinatum, localized lipoatrophy,^[5] congenital adrenal hyperplasia,^[6] polythelia,^[7] and accessory scrotum.^[8]

Becker nevus is considered a benign process; however, an association with melanoma was discussed in a series of 9 patients in whom both Becker nevus and melanoma developed. In this series, 5 patients developed melanoma on the same body site as the Becker nevus, but in 1 patient only did melanoma develop within the Becker nevus.

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Physical Examination

See History.

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Procedures

Skin biopsy provides histologic diagnosis of Becker nevus and helps distinguish it from other clinical entities.

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Histologic Findings

The epidermis demonstrates mild acanthosis and hyperkeratosis with regular elongation of rete ridges, as shown in the image below.

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Becker nevus demonstrating smooth muscle bundles in the dermis. Courtesy of Jason K. Rivers, MD.

The basal layer demonstrates hyperpigmentation resulting from increased melanin. Although often normal in number, an increase in the number of basal melanocytes occasionally can be detected.

Ultrastructurally, melanosomes are increased in keratinocytes, and giant melanosomes may be found in both keratinocytes and melanocytes.

Melanophages are present in the superficial dermis. Clinical hypertrichosis correlates with an increased number of morphologically normal follicular units. Almost every case demonstrates at least a slight increase in dermal smooth muscles.

Patches associated with smooth muscle hamartoma demonstrate more pronounced smooth muscle bundles irregularly dispersed within the dermis and unrelated to either hair follicles or vascular channels.

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Surgical Care

Therapeutic intervention for Becker nevus primarily is for cosmetic reasons. Patients present with complaints related to hypertrichosis and/or hyperpigmentation.

Q-switched ruby laser (694 nm) has been used with variable success in the treatment of both the hypertrichosis and hyperpigmentation of Becker nevus.^{[9, 10, 11]} Histopathologic analysis of lesional skin after laser treatment showed selective damage of superficially located melanocytes but a persistence of adnexal melanocytes. Remaining pigment cells may account for the transient improvement noted clinically.

A prospective study^[12] demonstrated the superiority of an Er:YAG laser (n= 11) over a Q-switched Nd:YAG system (n = 11) in the treatment of Becker nevus. Evaluation 2 years after treatment showed that 54% of subjects treated with the Er:YAG laser showed complete clinical clearance, while a clearance of greater than 50% occurred in 100% of the subjects. By comparison, none of the patients who received 3 treatments with the Nd:YAG laser system cleared completely and only one person had marked improvement. Supporting evidence for the role of the 2940-nm Er:Yag laser in the treatment of Becker nevus comes from a small case series from Saudi Arabia.^[13] Using this device, seven patients completed a single split-lesion treatment with follow-up to a year. All patients experienced some decrease in pigmentation in the range of 25-75%. Although the authors reported no hyperpigmentation or repigmentation, images from the paper show persisting depigmentation in the test areas performed prior to the full intervention in several of the subjects.^[13]

A long-pulsed 755-nm alexandrite laser was evaluated in 11 Korean patients with Becker nevus.^[14] Two patients had excellent responses, 5 had good responses, and 4 had fair responses. Hair density simultaneously decreased with treatment in all patients. Fifteen patients with Becker nevus underwent 8 sessions of hair removal with low-fluence, high-repetition-rate diode lasers (808-810 nm).^[15] All participants experienced significant hair reduction at 6 and 12 months, with no adverse events reported.

Eleven adult patients with Becker nevus were included in a prospective, randomized, controlled, observer-blinded, split-lesion trial. In each patient, 2 similar square test regions were randomized to either ablative factional laser therapy at 10 mJ/microbeam, coverage 35-45%, and topical bleaching (to reduce laser-induced postinflammatory hyperpigmentation), or topical bleaching alone. Treatment was moderately effective in some patients. However, postinflammatory hyperpigmentation and relatively negative patient-reported outcomes still preclude ablative fractional laser therapy from being a standard therapy.^[16] These results have been observed by this author, and the concern of both postinflammatory hyperpigmentation and hypopigmentation should be discussed with the patient prior to treatment. 

In 2016, three patients with Becker nevus (two hypertrichotic) were treated using a combination approach with a 1550-nm Er-doped nonablative fractional laser and a long-pulsed 1064-nm Nd:YAG laser in a sequential manner over time.^[17] Although these individuals had a clinical improvement of greater than 75%, follow up was limited (3-18 mo). Patients should be advised that over time (months to several years), pigment may recur at the treated site (author's personal observations).  

In sum, laser treatment of Becker nevus yields variable results and further studies are needed to determine the best way to reduce the appearance of these lesions without causing postlaser dyschromia or scarring.^[18]

Also see the Medscape article Laser Treatment of Benign Pigmented Lesions.

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