Hypomelanosis of Ito

Hypomelanosis of Ito is a descriptive term for a pattern of hypopigmented streaks and whorls following the lines of Blaschko, with a risk of extracutaneous involvement. It is a sign of mosaicism, not a single disease.

It is rare (about 1 in 8,000 to 10,000 children), with a slight female predominance. The pigment pattern is present at birth or in the first months of life.

About 30 to 75% of patients with this pattern have extracutaneous involvement, mainly neurological (seizures, developmental delay, intellectual disability), musculoskeletal (asymmetry, scoliosis) and ocular problems.

Pathophysiology.

Chromosomal mosaicism (including structural changes and trisomies) and mosaic single gene variants are found in many patients. The lines of Blaschko represent clones of cells that migrate during embryonic development, so the pattern marks the area of mosaicism.

• Hypopigmented, linear, patterned or whorled streaks on the trunk and limbs, often unilateral, without preceding inflammation or atrophy. Face and palms are less often affected.
• Seizures, developmental delay, microcephaly or macrocephaly, hypotonia and autism spectrum features.
• Limb length discrepancy, scoliosis, strabismus, myopia, dental anomalies and hair changes.

Red flags.

• Seizures, developmental regression or abnormal head size in an infant.
• Cardiac murmur, asymmetry of body growth or ocular problems.

• Clinical diagnosis from the pigment pattern, with a Wood's lamp in fair skin.
• Chromosomal analysis (blood and, if normal, cultured skin fibroblasts from a hypopigmented area), and chromosomal microarray or gene panels.
• Brain MRI and electroencephalography for neurological signs, ophthalmology, and developmental and orthopaedic assessment.

Differential diagnosis.

• Segmental vitiligo, naevus depigmentosus and naevus anaemicus.
• Incontinentia pigmenti (stage 4 hypopigmentation), tuberous sclerosis (ash leaf macules) and piebaldism.
• Post-inflammatory hypopigmentation and pigmentary mosaicism of other types.

• Explain the condition to parents, including the chance of other problems and the generally stable skin pattern.
• Treat seizures (anticonvulsants selected by seizure type), provide early developmental support, and manage orthopaedic and ocular problems.
• No treatment for the pigment is needed. Sun protection of hypopigmented skin and camouflage cosmetics. Excimer laser or narrowband ultraviolet B may help some patients.
• Genetic counselling (usually low recurrence risk).

Monitoring. Developmental review every 6 months in early childhood, then yearly, and vision checks.

Referral and escalation. Paediatric neurology, genetics, ophthalmology and orthopaedics as indicated.