Dermal Melanocytosis (Mongolian Spot)

Definition

• Benign dermal melanocyte entrapment occurring during embryogenesis

• Presents as flat, bluish-grey macules resembling bruises

• Commonly located on the lower back and buttocks, but may also appear on shoulders or limbs

Epidemiology

• Prevalent in infants of Asian, African, Indigenous Australian, and other darker-skinned backgrounds

• Uncommon in lighter-skinned infants

• Often present at birth or appearing within the first few weeks of life

Appearance

• Flat, non-tender, well-demarcated patches with a bluish-grey hue

• Typically asymptomatic and do not cause discomfort

• May vary in size and number, but remain stable unless noted otherwise

Differential Diagnosis

• Bruising or non-accidental injury when lesions appear extensive or in unusual locations

• Other congenital lesions including melanocytic naevi or café-au-lait macules

• Thorough history and examination help distinguish these lesions from trauma

Management

• No intervention required as lesions are non-progressive and pose no malignancy risk

• Spontaneous resolution by approximately 4 years of age for most, though some may persist into adolescence or adulthood in a faint form

• Emphasise to caregivers the benign nature and typical fading pattern

Documentation

• Important to record lesions clearly in the child’s medical file

• Prevents confusion with potential bruises in cases of suspected non-accidental injury

• Advise review only if atypical features arise, such as rapid enlargement or unusual colour changes

Notes

• Investigate further if there are concerns about possible abuse or if the lesion shows unexpected changes

• Reassure families that dermal melanocytosis does not transform malignantly and requires no treatment unless clinically atypical