Becker's nevus (Becker's melanosis, Becker's pigmentary hamartoma, nevoid melanosis, pigmented hairy epidermal nevus)

Are You Confident of the Diagnosis?

Becker’s nevus is a cutaneous hamartoma composed of hair follicles and arrector pili muscles and is not a true nevomelanocytic lesion. Hence the term, Becker’s nevus, is actually a misnomer. The diagnosis of Becker’s nevus is typically made clinically, although a biopsy may be necessary in some cases to differentiate the lesion from congenital melanocytic nevus.

What you should be alert for in the history

Becker’s nevus usually presents as a unilateral, hyperpigmented, hypertrichotic patch (Figure 1), with onset in early adulthood, usually during or shortly after puberty. To help differentiate it from congenital melanocytic nevus and smooth muscle hamartoma, it is important to ask whether the lesion was present at birth or developed subsequently.

Figure 1.

During puberty there is often a period of androgen-dependent lateral growth and darkening of hairs lasting for several years before stabilization. Although some patients report pruritus, the lesions are usually asymptomatic and brought to the attention of the physician for cosmetic concern.

Reported cutaneous findings within Becker’s nevi include acneiform eruptions, eczematous dermatitis, tinea versicolor, ichthyosis, and lichen planus. Patients may complain of symptoms from any of these co-localized disorders.

Characteristic findings on physical examination

On physical examination, most lesionsare localized, unilateral macules, patches, or very thin plaques. Theyare most frequently located on the shoulders, anterior chest, andscapular region, although numerous sites have been reported.

Lesionsrange in color fromlight tan to dark brown and are usually uniform inpigmentation. There is often an irregular, sharply demarcated borderthat resolves into small satellite islands of hyperpigmentation. Lesionsrange in diameter from a few centimeters to greater than 20 cm.

Hypertrichosisis a characteristic finding and tends to develop after pigmentation(sometimes up to 2 years later), with the hairs becoming coarser anddarker over time. In some cases the hypertrichosis may be subtle (Figure 2) or even absent (Figure 3).

Figure 2.

Figure 3.

Expected results of diagnostic studies

Histologicconfirmation of the diagnosis is generally unnecessary unless thelesion cannot be differentiated from a congenital melanocytic nevusbased upon clinical characteristics. Histologic findings include basalhyperpigmentation that may be subtle or easily discernible, withabnormal to minimally increased number of basilar melanocytes and noevidence ofmelanocytic nests.

There is variablehyperkeratosis, acanthosis, and elongation and focal fusion of the reteridges. The rete bases are often flattened and appear to have arectangular or square shape that is best appreciated on low-powerexamination and can help to establish the diagnosis inthe absence ofother histologic findings (Figure 4). Increased number of arrector pilimuscles may be seen and represents the smooth muscle hamartomatouscomponent of the Becker’s nevus (Figure 5).

Figure 4.

Figure 5.

Thedegree of basal pigmentation, number of hair follicles and smooth musclevaries significantly, and the biopsy may be interpreted as normal skinif the dermatopathologist is unaware of the clinical history. Inaddition, there may be a concomitant suppurative folliculitis with orwithout rupture and surrounding suppurative granulomatous inflammation.

Diagnosis confirmation

Thedifferential diagnosis includes congenital melanocytic nevus, congenitalsmooth muscle hamartoma, nevus spilus, and café au lait macules.

Congenitalmelanocytic nevi are present at birth and are typically darker incolor, raised, have no anatomic predilection and demonstrate melanocyticnevus cells on skin biopsy.

Congenital smoothmuscle hamartoma typically presents at birth or infancy as a firmskin-colored or light brown plaque. It has less prominent pigmentationand hypertrichosis when compared with Becker’s nevus, and most casesdisplay pseudo-Darier’s sign, temporary induration after rubbing thelesion. Histologically, smooth muscle hamartoma is characterized byhyperplasia of smooth muscle bundles throughout the dermis. Becker’snevus has more pronounced epidermal changes and a varying smooth musclecomponent within the dermis.

Nevus spilustypically contains several hyperpigmented macules and papules thatrepresent small melanocytic nevi distributed within a café au lait-likebackground that helps differentiate it from the uniformly pigmentedBecker’s nevus. Café au lait macules are usually smaller, lack terminalhairs and most often exhibit fairly uniform light brown color.

Who is at Risk for Developing this Disease?

The prevalence of Becker’s nevus is estimated to beapproximately 0.5% among males. The male-to-female ratio derived from reported cases is approximately 6:1. This higher male-to-female ratio has been attributed to greater recognition of lesions in males due to androgen-dependent growth. Lesions in females tend to have lighter pigmentation and absent or subtle hypertrichosis and are therefore likely to be underreported.

The lesion has been described in all races and nearly all cutaneous surfaces. Most lesions present within the first 2 decades, typically around puberty, although congenital cases have been reported. Most cases are sporadic, but several familial cases have been described.

What is the Cause of the Disease?

Etiology

The etiology of Becker’s nevus remains unclear. It is a hamartoma of ectodermal and mesodermal derivatives that is thought to be hormonally responsive given the augmented smooth muscle and peripubertal growth. Androgen receptor assays have demonstrated marked increases in the number of androgen receptors in lesional skin when compared with contralateral non-lesional skin.

Additional evidence supporting heightened sensitivity to androgens includes the findings of hypertrichosis, acanthosis, dermal thickening, sebaceous hypertrophy and co-localized acne.

Numerous cases, including two originally described by Becker, have been reported to occur after sunburn or extensive sunlight exposure and therefore this could represent an additional trigger.

Pathophysiology

Thedevelopmental anomalies associated with Becker’s nevus syndrome,including breast hypoplasia, supernumerary nipples and musculoskeletalanomalies, are similar to the spectrum seen in the epidermal nevussyndrome and suggest mosaicism. In fact, chromosomal mosaicism has beendocumented in fibroblasts derived from a Becker’s nevus in one case.

Anotherreported case of Becker’s nevus identified in early childhood wasinitially verrucous and linear before becoming hyperpigmented andhypertrichotic after puberty, suggesting an initial mosaic patternfollowing the lines of Blaschko.

Because Becker’snevus has both familial and sporadic occurrence, some authors suggest aparadominant inheritance with loss of heterozygosity resulting in amosaic population of homozygous or hemizygous cells.

Systemic Implications and Complications

The Becker’s nevus itself is a benign lesion, although an association between Becker’s nevus and developmental anomalies has been reported. By far the most commonly reported associated anomaly is ipsilateral breast hypoplasia. In one study this occurred more frequently among women than men at a ratio of approximately 4:1. The higher reported incidence among women is likely because breast hypoplasia is more conspicuous in women.

Hypoplasia of the breast can best be explained by the excess androgen receptors within lesional skin counteracting the estrogen-dependent development of breast, areola and nipple at puberty. Spironolactone treatment resulted in enlargement of the hypoplastic breast in one study.

Other reported anomalies include scoliosis, vertebral anomalies, limb asymmetry, fused or accessory ribs, facial asymmetry, odontomaxillary dysplasia, asymmetry of the scapulae, hypoplasia of the contralateral labium minus, decreased hairiness of the ipsilateral axilla, accessory scrotum, and supernumerary nipples. Similar anomalies are also seen in epidermal nevus syndromes, and some authors consider Becker’s nevus to be an organoid type of epidermal nevus sharing molecular mosaicism as the underlying etiology.

Treatment Options

Table I. Treatment options for Becker’as nevus