Dermal melanocytosis (Mongolian spot)
Mongolian spot; congenital dermal melanocytosis; slate-grey naevus of infancy
Dermal melanocytosis is a common congenital blue-grey to slate-grey macular pigmentation of the lumbosacral region (occasionally elsewhere) caused by the persistence of dermal melanocytes that failed to migrate to the dermoepidermal junction during embryogenesis. It is present at birth in approximately 80–90% of Fitzpatrick IV–VI infants and fades spontaneously over the first decade. Although uniformly benign, its bruise-like appearance is a recurrent cause of misinterpretation in safeguarding assessments — accurate documentation at the newborn examination protects families from inappropriate child-protection referrals. Persistence of extensive or aberrantly distributed dermal melanocytosis can rarely be associated with phakomatosis pigmentovascularis or lysosomal storage disorders.
Clinical features
- Blue-grey to slate-grey, non-blanching macule or patch, ill-defined edge.
- Most commonly lumbosacral or buttocks; less commonly upper back, shoulders or extremities.
- Present at birth in ~ 80–90% of Fitzpatrick IV–VI infants; 1–10% of Fitzpatrick I–III infants.
- Lesions fade gradually over the first 5–10 years and resolve completely in most cases.
- Aberrant dermal melanocytosis — extensive, persistent or unusually distributed lesions — should prompt consideration of an underlying syndrome.
Differential — including the bruise question
- Bruise / non-accidental injury — bruises evolve through colour change (red → blue → green → yellow) over days; dermal melanocytosis is stable and present from birth.
- Document the size, location, colour and stable nature of Mongolian spots at the newborn examination and again on routine reviews — this is the most powerful protection against safeguarding misinterpretation.
- Blue naevus — discrete blue papule, not congenital, dermal melanocyte aggregation.
- Naevus of Ota — dermal melanocytosis of the trigeminal region.
- Naevus of Ito — dermal melanocytosis of the supraclavicular / deltoid region.
- Phakomatosis pigmentovascularis — combined dermal melanocytosis with capillary malformation; rarely associated with neurological abnormalities.
Syndromic associations (rare)
- Phakomatosis pigmentovascularis (types II/III) — combined dermal melanocytosis and vascular malformation; ophthalmological / neurological surveillance.
- Lysosomal storage disorders — GM1 gangliosidosis, Hurler syndrome, Hunter syndrome — extensive or persistent dermal melanocytosis has been reported with developmental delay and dysmorphism.
- Cleft lip/palate associations have been described.
- Most cases are isolated and benign.
Management
- No treatment required for classical lesions — reassurance and documentation.
- Photographs and clinical notes at newborn check and Health Visitor reviews — essential safeguarding protection.
- Q-switched laser therapy (1064 nm Nd:YAG, 755 nm alexandrite) is occasionally used for persistent cosmetically problematic facial lesions, with variable efficacy.
- Persistent extensive lesions warrant assessment for syndromic associations.
References
- Cordova A. The Mongolian spot — a study of ethnic differences and a literature review. Clin Pediatr; 1981.
- Gupta D, Thappa DM. Mongolian spots — a prospective study. Pediatr Dermatol; 2013.
- Royal College of Paediatrics and Child Health. Safeguarding children and young people and children and young people in care: competencies for health care staff. Intercollegiate document, 5th ed.; 2025.
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