Becker's Naevus

Synonyms: Becker's nevus, melanosis neviformis

This is so called after S. William Becker who in 1948 described 2 young men with acquired melanosis and hypertrichosis distributed unilaterally. It is recognised as a form of benign late onset birth mark, usually noticed around puberty (early teens) as an irregular well demarcated hyperpigmented patch, occurring on one side of the body only. The patch may extend and become both quite large and hairy, but remains fixed in site. Sometimes just an increased amount of hair is noticed. Lesions usually occur over the upper trunk or shoulders.¹

• Prevalence is 0.52% in a group of men aged 17-26 years.²
• Men are more often affected than women.

• They present as asymptomatic irregular light brown (tan) patches found usually on the shoulder, upper chest, or back.
• Onset is most often in the peripubertal period.
• The patch expands over several years. New irregular pigmented macules and patches develop around the larger patch and eventually join or coalesce with it.
• Ultimately they may thus cover a large area.
• Months or years after the appearance of pigmentation thick dark hairs develop in and around the patch. The amount of hair is variable and occasionally hair (hypertrichosis) is not found.
• The central area in the patch may thicken.
• Acne vulgaris may develop within the patch.
• Some fading (reduced pigmentation) may occur in adulthood.

The age of onset, site and the fixed nature of the lesion is usually enough to make the diagnosis.

Pityriasis versicolor is usually symmetrical and slightly scaly, while post inflammatory hyperpigmentation is poorly defined.

If the lesion is non-hairy, consider café au lait patch or postinflammatory hyperpigmentation.²

It is occasionally associated with a smooth muscle hamartoma,³ and rarely hypoplasia or aplasia of the structures under the skin has been reported (e.g. breast or pectoralis major hypoplasia, limb shortening).² Associated congenital adrenal hyperplasia has been reported.

Although Becker's naevus is a benign lesion, there is an association between Becker's naevus and malignant melanoma occurring in the same patient, and one reported case of a cutaneous melanoma developing within a Becker's naevus.^2,4

The epidermal layer shows mild acanthosis and hyperkeratosis with a regular elongation of rete ridges; whilst the basal layer shows increased melanin (hyperpigmentation).²

• No treatment is necessary except for cosmetic reasons; usually reassurance and a diagnosis is enough.
• Electrolysis may help with hair removal.
• Laser removal can be successful. Er:YAG laser (n= 11) may be superior.²
• If there is doubt about the diagnosis (e.g. possible melanoma) urgent referral is appropriate.

It remains indefinitely.¹

For confirmation of diagnosis and cosmetic removal.