Atypical / Dysplastic Naevus — SAQ

Stem

A 28-year-old woman presents for routine skin check. She has more than 60 melanocytic naevi scattered over her trunk and limbs, of which at least 8 are clinically atypical (irregular borders, colour variegation, diameter >5 mm). Her father developed melanoma at age 42 and died of metastatic disease at age 50. She has one atypical naevus on her back that looks darker and more irregular than her other naevi.

Questions

a) What is the most likely clinical syndrome in this patient, and what is the underlying genetic abnormality? (2 marks)

b) Describe the clinical features of an atypical (dysplastic) naevus and the ABCDE criteria. (3 marks)

^[2]c) Outline the initial management and investigations for this patient. (3 marks)

d) The atypical naevus on her back is biopsied and reported as "severely dysplastic naevus with positive margins." How would you manage this result? (2 marks)

^[1]

Model answer

a) Syndrome and genetics (2 marks)

• The patient has familial atypical multiple mole melanoma (FAMMM) syndrome: more than 50 naevi, at least 5 clinically atypical, plus a first-degree relative with melanoma. (1 mark)
• It is associated with germline mutations in CDKN2A (encoding p16INK4a and p14ARF tumour suppressors). (1 mark)

^{[2] [4]}

^[3]b) Clinical features and ABCDE criteria (3 marks)

• Atypical naevus features: larger than common naevi (often >5 mm), irregular border, colour variegation, macular/papular or target-like/fried-egg appearance, may be asymmetrical. (1 mark)
• ABCDE: Asymmetry, Border irregularity, Colour variegation, Diameter >5 mm, Evolution/change. (2 marks if all five listed correctly)

^[2]c) Initial management and investigations (3 marks)

• Full skin examination with dermoscopy; identify the "ugly duckling" lesion (the one that looks different from the others). (1 mark)
• Baseline total body photography and sequential digital dermoscopy for high-risk lesions. (1 mark)
• Genetic counselling for CDKN2A testing; consider pancreatic cancer screening as advised by the genetics service; intensive dermatology surveillance; patient education on self-examination and sun protection. (1 mark)

^[2][5]d) Management of severely dysplastic naevus with positive margins (2 marks)

• Re-excision is advised because severe dysplasia is difficult to distinguish from melanoma in situ and the lesion may be a true precursor. (1 mark)

^[1]

• Ensure clinical-histological correlation; if the lesion looked clinically suspicious for melanoma, manage with a low threshold for wider excision and sentinel lymph node discussion if invasive melanoma is subsequently confirmed. (1 mark)

References5ShowHide

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