Becker's Naevus

Synonyms: Becker melanosis, pigmented hairy naevus of Becker

What is Becker's naevus?

Becker's naevus is a form of epidermal naevus (birthmark). It usually appears around puberty as a hyperpigmented patch, most often found on the upper trunk or shoulders.^{[1, 2, 3]}

See also the article on Epidermal Naevus and its Syndromes.

Becker's naevus on shoulder

Jmarchn, CC BY-SA 3.0 , via Wikimedia Commons

Aetiology^[1]

There is overgrowth of the epidermis (upper layers of the skin), pigment cells (melanocytes) and hair follicles. It may be due to a gene defect (as yet unidentified), perhaps triggered by circulating androgens, which would explain its onset during adolescence.

How common is Becker's naevus? (Epidemiology)^[1]

• More common in males (ratio of 5:1). The estimated prevalence among males is 1 in 200.
• Can occur in all skin types.
• Usually presents in the second or third decade of life.

Becker's naevus symptoms (presentation)^{[1, 2]}

• A large brown area, sometimes covering half the upper back or chest. Most lesions become hairy (hypertrichosis).
• After puberty it often becomes darker and expands, usually over a period of 1-2 years.
• Occasionally acne may develop in the naevus.
• Some fading (reduced pigmentation) may occur in adulthood.
• One case of bilateral, symmetrical pigmentation is reported - this is unusual.^[3]

Diagnosis

The age of onset, site and the fixed nature of the lesion are usually enough to make the diagnosis. Biopsy may occasionally be needed.

Differential diagnosis^[1]

• McCune-Albright syndrome (with café-au-lait patches on the skin).
• Pityriasis versicolor is usually symmetrical and slightly scaly.
• Congenital melanocytic naevus.

Histology^{[3, 4]}

• Epidermis: acanthosis and hyperpigmentation of the basal layer, with elongation and fusion of adjacent rete ridges and variable hyperkeratosis.
• Dermis: hyperplasia of the dermal smooth muscle and melanophages.

Becker's naevus treatment and management^[1]

• No treatment is necessary except for cosmetic reasons; usually reassurance and a diagnosis are enough.
• For cosmetic treatment of the lesion:
  • Electrolysis or laser treatment may help with hair removal.
  • Laser treatment can sometimes reduce the pigmentation, but may be ineffective or may worsen the lesion.
  • Fractional resurfacing has also been used to lighten the lesions.^[3]
• For acne in the lesion, use standard acne treatments.
• If there is doubt about the diagnosis (eg possible melanoma), urgent referral is appropriate.

Prognosis

The naevus remains indefinitely. There are no reports of Becker naevi undergoing malignant changes.^[5]

Becker naevus syndrome^{[5, 6]}

Becker's naevus syndrome is a type of epidermal naevus syndrome. It is characterised by the presence of a Becker's naevus with ipsilateral breast hypoplasia or hypoplastic defects of the muscle, skin, or skeleton.

The naevus usually consists of a circumscribed, unilateral, irregularly shaped hyperpigmented macule, commonly occurring around the anterior upper trunk, with/without hypertrichosis and/or acneiform lesions.

Other features may include:

• Supernumerary nipple.
• Loss of subcutaneous fat
• Loss of axillary hair
• Musculoskeletal abnormalities and asymmetry.