Atypical / Dysplastic Naevus — Viva

Q1: Definition and clinical features (2 min)

What is an atypical (dysplastic) naevus? How does it differ clinically and histologically from a common melanocytic naevus?

Model answer: An atypical naevus is a benign melanocytic naevus with clinical features of irregularity (asymmetry, irregular border, colour variegation, diameter >5 mm) and/or histological features of architectural disorder and cytological atypia. The term "atypical" is clinical; "dysplastic" is histological. A clinically atypical naevus may be histologically banal, and vice versa. Histologically, dysplastic naevi show bridging, shouldering, lamellar fibrosis, and cytological atypia graded mild, moderate, or severe.

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Q2: Risk stratification and epidemiology (3 min)

How do you classify atypical naevi by clinical context, and what is the melanoma risk in each category?

Model answer: Three categories of increasing melanoma risk: (1) Sporadic isolated atypical naevus — modestly increased risk; (2) Atypical mole syndrome — many naevi with several atypical lesions but no family history — substantially higher risk; (3) FAMMM syndrome — many atypical naevi plus a first-degree relative with melanoma, often linked to a germline CDKN2A mutation — highest risk, with an associated pancreatic cancer risk. Risk rises with fair skin, UV exposure, high naevus count, and immunosuppression.^[2][3][4]

Q3: Differential diagnosis and investigations (3 min)

How would you distinguish an atypical naevus from melanoma? What investigations help?

Model answer: Melanoma evolves rapidly, shows marked asymmetry, blue-white veil, polymorphous vessels, regression, and ulceration on dermoscopy, and histologically shows pagetoid spread, dermal mitoses, and Breslow thickness. Atypical naevus is stable, lacks these melanoma-specific features, and histologically shows limited junctional atypia without pagetoid spread or dermal mitoses. Investigations: dermoscopy, sequential digital dermoscopy, total body photography, excisional biopsy for suspicious lesions, and CDKN2A genetic testing in FAMMM families.^[2][3]

Q4: Management (3 min)

A patient with FAMMM syndrome asks whether all her atypical naevi should be removed. How do you counsel and manage her?

Model answer: Prophylactic excision of all atypical naevi is not recommended because most melanomas (about 70% in meta-analysis) arise de novo rather than from a pre-existing naevus, and mass excision does not reduce mortality.^[6] Management is risk-stratified surveillance: total body photography, sequential digital dermoscopy, dermatology review every 3–6 months, monthly self-examination, sun protection, genetic counselling, and pancreatic cancer screening as advised by the genetics service. Biopsy only changing, suspicious, or ugly-duckling lesions.

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Q5: Histology and follow-up (2 min)

A dysplastic naevus is reported as "moderately dysplastic with positive margins" and there is no residual clinical pigment. What is your management? What if it were severely dysplastic?

Model answer: Moderate dysplasia with positive margins and no residual pigment: observation is reasonable based on the Pigmented Lesion Subcommittee consensus and subsequent data. If severe dysplasia: re-excision is advised because the lesion may represent melanoma in situ or early melanoma and the diagnosis can be difficult. Clinical suspicion always trumps histology; if the lesion looked suspicious, re-excise or re-biopsy regardless of the reported grade.

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Q6: Examiner probe (2 min)

Why is the ugly duckling sign more useful than applying ABCDE to every naevus in a patient with many atypical naevi?

Model answer: Each person has a characteristic naevus pattern. The outlier — the ugly duckling — is more likely to be melanoma. Applying ABCDE to hundreds of lesions is insensitive and overwhelming; the ugly duckling sign allows rapid identification of the one lesion that needs attention. Most melanomas (about 70% in meta-analysis) arise de novo rather than from a pre-existing naevus, so detecting change and identifying outliers is more effective than counting naevi.^[5][6]

References6ShowHide

1. [1]Kim CC, Swetter SM, Curiel-Lewandrowski C, et al. Addressing the knowledge gap in clinical recommendations for management and complete excision of clinically atypical nevi/dysplastic nevi: Pigmented Lesion Subcommittee consensus statement JAMA Dermatol, 2015.PMID 25409291
2. [2]Drozdowski R, Spaccarelli N, Peters MS, et al. Dysplastic nevus part I: Historical perspective, classification, and epidemiology. Journal of the American Academy of Dermatology, 2023.PMID 36038073
3. [3]Friedman RJ, Farber MJ, Warycha MA, et al. The 'dysplastic' nevus. Clinics in Dermatology, 2009.PMID 19095156
4. [4]Newton-Bishop J, Bishop DT, Harland M. Melanoma Genomics. Acta dermato-venereologica, 2020.PMID 32346746
5. [5]Gaudy-Marqueste C, Wazaefi Y, Bruneu Y, et al. Ugly Duckling Sign as a Major Factor of Efficiency in Melanoma Detection. JAMA Dermatol, 2017.PMID 28196213
6. [6]Pampena R, Kyrgidis A, Lallas A, et al. A meta-analysis of nevus-associated melanoma: Prevalence and practical implications. J Am Acad Dermatol, 2017.PMID 28864306