Linear and Whorled Naevoid Hypermelanosis

Linear and whorled naevoid hypermelanosis is a benign pigmentary disorder with streaks and whorls of hyperpigmentation that follow the lines of Blaschko, without preceding inflammation, vesicles or atrophy.

It is rare. It appears in the first weeks or months of life, expands during the first year or two, and then stabilises. Both sexes are affected equally.

Most patients have only skin involvement. Neurological, skeletal and other anomalies are reported in some patients (up to a quarter), and may reflect chromosomal mosaicism.

Pathophysiology.

Genetic mosaicism, including chromosomal abnormalities such as trisomy 7, 14 or 18 and mosaic variants, leads to clones of melanocytes with increased pigment production that follow the lines of embryonic skin migration.

• Hyperpigmented streaks on the trunk and limbs in a V shape on the back, an S shape on the abdomen and linear on the limbs. The face, palms and soles are spared.
• The pigment is flat, without scale or atrophy, and may fade slowly in later childhood.
• Occasionally associated: seizures, developmental delay, hemiatrophy, scoliosis, cardiac defects or hearing loss.

Red flags.

• Developmental delay, seizures or a skeletal anomaly in an infant with the pigment pattern.

• Clinical diagnosis from age at onset and Blaschko pattern, with a history of no earlier blistering or inflammation.
• Skin biopsy if the diagnosis is uncertain: basal hyperpigmentation with no pigment incontinence and no inflammatory change.
• Neurological and developmental assessment. Chromosomal analysis (blood, and skin fibroblasts if blood is normal) and further imaging only if extracutaneous features are present.

Differential diagnosis.

• Incontinentia pigmenti (stage 3, with a preceding vesicular and verrucous phase).
• Epidermal naevus, naevus spilus and Becker naevus.
• Post-inflammatory hyperpigmentation and pigmentary mosaicism of other kinds (for example the reverse pattern of hypomelanosis).

• Reassure the family that the pigmentation is benign and tends to be stable or fade.
• No treatment is needed. Sun protection and camouflage cosmetics. Laser has uncertain effect.
• Developmental review and referral for extracutaneous features. Genetic counselling is offered when chromosomal mosaicism is identified (recurrence risk is low).

Monitoring. Developmental review every 6 to 12 months in early childhood.

Referral and escalation. Paediatrics, neurology or genetics for developmental delay, seizures or other anomalies.