Naevus depigmentosus (achromic naevus)

Definition

Naevus depigmentosus (achromic naevus) is a congenital or early-childhood, non-progressive hypopigmented patch that keeps its relative size and distribution throughout life and simply grows in proportion with the child. It is regarded as a form of cutaneous mosaicism. Unlike vitiligo, the patch is not completely devoid of pigment but only hypopigmented.

Classification

• Isolated type: a single circumscribed patch.
• Segmental type: sharp demarcation at the body midline with poorly defined lateral borders.
• Systematised (linear) type: follows Blaschko lines and overlaps clinically with hypomelanosis of Ito.

Occurrence & epidemiology

In a series of 67 patients the lesions were present before the age of 3 years in 92.5%; 59.7% had the isolated and 40.3% the segmental type; the back and buttocks were most commonly affected, followed by the chest and abdomen. In children with fair skin the patch may only become apparent in mid-childhood.

Clinical features

• Well-defined, off-white patch, often several centimetres across, with an irregular, sometimes serrated border; smaller satellite macules are common at the edge (like scattered splashes of paint).
• Mainly on the trunk; solitary in about half of cases.
• No change in skin texture or sensation, no dark border.

Diagnosis

• Clinical, using Coupe's criteria: present from birth or early childhood, unchanged location, no change in texture or sensation, no hyperpigmented border.
• Wood lamp: off-white, not chalk-white as in vitiligo.
• Dermoscopy: white structureless areas with a serrated border and pseudopod-like extensions, with a faint but preserved reticular pigment network.
• Biopsy (rarely needed): normal or slightly reduced melanocyte numbers with decreased melanin.

Differential diagnoses

• Vitiligo
• Hypomelanosis of Ito (incontinentia pigmenti achromians)
• Oculocutaneous albinism
• Piebaldism
• Pityriasis alba
• Nevus anemicus
• Idiopathic guttate hypomelanosis
• Progressive macular hypomelanosis

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References (selection)

1. DermNet: Achromic naevus (naevus depigmentosus)
2. DermNet: Dermoscopy of achromic naevus
3. PubMed: Nevus depigmentosus: clinical features and histopathologic characteristics in 67 patients (PMID 9922008)
4. PubMed: Clinical and histopathologic characteristics of nevus depigmentosus (PMID 16908347)

Cross-references