Acquired melanocytic nevi (common and dysplastic)
Acquired melanocytic nevi (moles) are benign melanocyte neoplasms that appear after the first months of life and increase in number until middle age; common nevi are small, symmetric, evenly colored, and stable, whereas dysplastic nevi are larger, irregular, and multicolored and mark a higher melanoma risk. A lesion with ABCDE features, change, symptoms, or an ugly duckling appearance gets an excisional biopsy with a 1 to 2 mm margin, and patients with dysplastic nevus syndrome get yearly total-body skin examinations.
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What this article covers
- Overview
Definition: acquired melanocytic nevi (moles) are benign neoplasms of melanocytes that develop after the first few months of life, which separates them from congenital melanocytic nevi present at or soon after birth.
- Epidemiology
Universal and age-dependent: nevi appear in early childhood and increase in number until middle age.
- Risk factors
Family history and inherited predisposition: familial and ultraviolet-related mechanisms drive acquired nevi, and familial atypical mole and melanoma syndrome (with CDKN2A or CDK4 mutations in some…
- Pathophysiology
Benign melanocyte proliferation: nevi are clonal nests of melanocytes, arising from familial and ultraviolet-related pathways rather than the embryonic neural crest migration error behind congenital nevi.
- Clinical features
Common nevus pattern: a small (usually under 6 mm), round, symmetric macule or papule with smooth regular borders and uniform tan, brown, or skin color that stays the same size and color and causes no symptoms.
- Differential diagnosis
Melanoma: a new or changing pigmented lesion with ABCDE features, an ugly duckling appearance, symptoms, or nodularity, confirmed only on histology (melanoma).
- Diagnosis
Common nevi are a clinical diagnosis, while a dysplastic nevus is confirmed and melanoma excluded only by histology: a symmetric, evenly colored, regularly bordered, stable, asymptomatic lesion…
- Management
First, leave stable benign-appearing nevi alone: a common nevus without ABCDE features, change, or symptoms needs no removal, and excision for cosmetic reasons is optional.
- Complications
Melanoma: the serious outcome, arising within a nevus uncommonly but at higher rates in patients with many or dysplastic nevi.
- Prognosis
Excellent for individual nevi: the risk that a single common or dysplastic nevus becomes melanoma is very small.
- Prevention
Use broad-spectrum sunscreen of SPF 30 or higher: apply about 2 mg/cm2 (roughly 30 mL for an adult's whole body) 15 to 30 minutes before exposure and reapply at least every 2 hours and after swimming, sweating, or towel-drying.
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