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Diagnosis of this condition
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The image shows a well-demarcated hypopigmented patch on the left lateral abdomen/flank of a child. Based on the clinical appearance and textbook evidence, here is the diagnosis and differential:
Diagnosis: Nevus Depigmentosus
(Most likely diagnosis based on the image)
Clinical Features Supporting This Diagnosis
- Well-demarcated hypopigmented (not depigmented) patch on the lateral abdomen - exactly as shown
- Congenital or appearing in early childhood - becomes more visible as background skin pigmentation increases in the first year of life
- Irregular border, often with satellite macules at the periphery ("splash of paint" appearance)
- Stable, non-progressive - grows only proportionally with the child
- No scaling, erythema, or surface change - it is a flat (macular) lesion
- Does NOT cross the midline (consistent with pigmentary mosaicism)
Pathophysiology
Nevus depigmentosus is considered a form of cutaneous mosaicism - a localized defect in melanin production/transfer in affected keratinocytes. Despite the name, it is actually hypopigmented (reduced pigment), not completely depigmented.
(Dermatology 2-Volume Set 5e, p. 1227; Fitzpatrick's Dermatology, p. 1763)
How to Distinguish From Key Differentials
| Feature | Nevus Depigmentosus | Nevus Anemicus | Vitiligo |
|---|---|---|---|
| Onset | Congenital / early childhood | Congenital | Any age |
| Pigment | Hypopigmented | Hypopigmented (vascular) | Completely depigmented (chalky white) |
| Diascopy (glass slide pressure) | Border remains sharp | Lesion disappears (blends with blanched surrounding skin) | Border remains sharp |
| Wood's lamp | Mildly enhanced | No enhancement | Markedly enhanced (chalk-white) |
| Surface | Normal | Normal | Normal |
| Cause | Melanin defect | Focal catecholamine hypersensitivity | Autoimmune melanocyte destruction |
(Fitzpatrick's Dermatology, Table 103-3)
Important Note - Rule Out Tuberous Sclerosis
"Three or more nevus depigmentosus/hypomelanotic patches in a newborn should prompt evaluation for possible tuberous sclerosis complex."
- Fitzpatrick's Dermatology, p. 1763
If this child has 3 or more such patches, evaluate for tuberous sclerosis (also look for ash-leaf macules, shagreen patches, adenoma sebaceum, seizures, developmental delay).
Management
- No treatment required - this is a benign, stable birthmark
- Confirm diagnosis with Wood's lamp examination (mild enhancement, vs. bright chalk-white in vitiligo)
- Diascopy to exclude nevus anemicus
- Reassure the family - the patch will not spread and poses no health risk in isolation
- Refer to a pediatric dermatologist if diagnosis is uncertain or if multiple such patches are present
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