Dysplastic (atypical) naevus
Atypical melanocytic naevus; Clark naevus; dysplastic naevus syndrome; FAMMM
Atypical / dysplastic naevi are melanocytic naevi with clinical and histological features intermediate between common naevi and melanoma. Most are benign and stable; rarely an individual lesion progresses to melanoma. The patient with multiple atypical naevi is at materially increased melanoma risk and warrants surveillance.
Clinical features
Classic features ('clinical atypia'):
- Diameter ≥6 mm.
- Variable pigmentation (typically two or more shades of brown).
- Indistinct or hazy peripheral border (macular component).
- Central papule with macular periphery — 'fried-egg' appearance.
- Often multiple in patients with naevus-prone skin.
FAMMM / dysplastic naevus syndrome
The combination of multiple atypical naevi, family history of melanoma and personal melanoma history defines the FAMMM syndrome (familial atypical multiple mole melanoma). Lifetime melanoma risk approaches 70%+ in CDKN2A carriers (see familial melanoma monograph).
Dermoscopy
Most atypical naevi show symmetric or mildly asymmetric pigment network with regular peripheral globules. Concerning features (see dermoscopy reference): atypical network, blue-white veil, regression, atypical vessels, asymmetric streaks. Sequential dermoscopy (digital monitoring) is the standard for following multiple atypical naevi.
Management
- Excise the most atypical lesion with a 2 mm narrow margin if there is genuine dermoscopic concern.
- For patients with multiple atypical naevi: total-body photography + sequential digital dermoscopy at 3–6 month intervals.
- Patient education: self-examination, partner-assisted exam, ABCDE / ugly duckling, sun protection from infancy, sunbed avoidance.
- Avoid prophylactic excision of all atypical naevi — the risk per lesion is small and burden of surgery substantial.
- Refer to clinical genetics if FAMMM criteria met (≥3 melanomas in family, ≥2 melanomas in one individual, melanoma + pancreatic cancer, melanoma + uveal + mesothelioma → see familial melanoma).
Histological dysplasia grading (mild / moderate / severe) is poorly reproducible and inconsistently translated to clinical management. UK practice: complete excision (clear margin) for moderately or severely dysplastic naevi; observation acceptable for mildly dysplastic naevi with clear margin.
References
- Soura E et al. Hereditary melanoma: update on syndromes and management. J Am Acad Dermatol; 2016.
- Naeyaert JM, Brochez L. Dysplastic nevi. N Engl J Med; 2003;349:2233–40.
- Tucker MA et al. Clinically recognized dysplastic nevi: a central risk factor for cutaneous melanoma. JAMA; 1997;277:1439–44.
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