Melanocytic Nevi Emerging in Infancy
Yes, infants can develop congenital melanocytic nevi (CMN) that become visible after birth, typically appearing within the first several months of life, though these melanocytes were present from birth even if not initially visible. 1
Understanding Post-Birth Appearance of CMN
The term "congenital" can be misleading because CMN typically present at birth, although some appear after several months and are still considered congenital in origin. 1 This delayed visibility creates diagnostic challenges:
- Estimates of CMN incidence are limited by age at examination, with reports on neonates potentially missing CMN that become visible only after birth 1
- Studies of older children may include more nevi than are truly congenital based on recall bias and appearance 1
- The reported incidence of CMN varies widely from <1% to 31.7%, though most studies calculate 1-3.6% 1, 2
Evolution and Changes Over Time
CMN undergo expected benign changes during infancy and childhood that should not cause alarm:
- Pigmentation may become more mottled or speckled 1, 3
- Surface characteristics can become more raised, papillated, or develop hypertrichosis (increased hair growth) 1, 3
- Some nevi spontaneously lighten over time, particularly scalp CMN, though nevus cells remain histologically present 1
- Changes can include homogeneous or heterogeneous darkening or lightening 1
Clinical Implications for Monitoring
Parents and providers should understand that CMN may change over time, making continued monitoring important 1:
- Hypertrichosis may be present at birth or develop later 1
- CMN typically grow in proportion to a child's somatic growth 1
- Expected changes differ from concerning changes that warrant evaluation 1, 3
When to Seek Evaluation
Parents should monitor nevi visually and with palpation between visits and report concerning changes 1, 2:
- Rapid growth (beyond proportional somatic growth)
- Bleeding or ulceration
- Pain or development of nodules
- Asymmetric growth or color variation 3
These concerning changes should be promptly evaluated by a dermatologist, as they may represent proliferative nodules (benign secondary growths) or, rarely, melanoma 1
Distinction from Acquired Nevi
It's important to distinguish CMN appearing after birth from truly acquired melanocytic nevi that develop during childhood and adolescence. Most melanocytic nevi develop during childhood and adolescence with stabilization by middle age (around 25 years old) 4, but these are distinct from CMN that were present embryologically but became visible postnatally.