Becker's Naevus

Synonyms: Becker melanosis, pigmented hairy naevus of Becker

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]}

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.

Epidemiology

• It is more common in men.
• One study reported a prevalence of 0.52% in men aged 17-26 years.^[4]

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.

Differential diagnosis^[5]

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

Histology^{[3, 6]}

• 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.

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.^[2]

Becker naevus syndrome^{[1, 6, 7]}

This is a Becker's naevus with additional abnormalities of underlying tissues derived from ectoderm. It is a type of epidermal naevus syndrome. There may be underdevelopment or overdevelopment of underlying structures, including:

• Smooth muscle hamartoma.
• Hypoplasia of breast.
• Spina bifida or scoliosis, pectus carinatum, pectus excavatum.
• Adrenal hyperplasia.
• Asymmetry of limbs, trunk or face.
• Umbilical hernia.
• Supernumerary nipple, accessory scrotum.

History

It is named after S. William Becker who first described the lesion in 1949. Becker naevus syndrome was described in 1995 by Happle.