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Atypical nevus syndrome in Adult
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Atypical nevus syndrome in Adult

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Contributors: Ansa Ahmed MD, Art Papier MD
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Atypical nevus syndrome is a term used to describe patients who have multiple nevi covering their body and a history of melanoma in the family (eg, in parents, siblings, grandparents, aunts, uncles). The features of this syndrome are threefold: the nevi number 100 or more, at least one nevus is 5 mm or greater in diameter, and at least one nevus has atypical features.

The nomenclature regarding atypical nevi is confusing, but atypical melanocytic nevus (AMN), formerly referred to as atypical (dysplastic) nevus, is the most common term used today. Atypical nevus is also known as Clark nevus, atypical mole, B-K mole, and mole of FAMM (familial atypical mole and melanoma syndrome).

Common nevi are macular or papular symmetrical lesions that are smaller than 5 mm and have well-defined borders that are uniform in color. Atypical nevi, in contrast, have irregular colors and shapes and indeterminate borders. If one examined an isolated atypical nevus in a patient with atypical nevus syndrome, one would be suspicious for melanoma because of the striking irregular features of color, shape, and large size. At the onset, atypical nevi appear as ordinary small, symmetrical nevi, but they continue to grow over time – in contrast to other nevi – and develop blurred borders and asymmetry. Nevi may also appear atypical from the onset.

The risk of developing melanoma is related to a number of factors, which include:
  • Number of ordinary nevi being more than 50-100 on the body.
  • The presence of and number of atypical nevi.
Patients with atypical nevus syndrome are at high risk for developing melanoma. Past history of melanoma or melanoma in other family members dramatically increasess the risk manifold. Melanoma does not have to develop in already existing nevi. It may occur elsewhere on the body.

The incidence of atypical nevus syndrome has been reported to be around 5%.


D23.9 – Other benign neoplasm of skin, unspecified

254819008 – Atypical mole syndrome

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Differential Diagnosis & Pitfalls

Atypical nevus syndrome is unique because the numbers help define the diagnosis. The individual nevus has to be differentiated from melanocytic and keratinocytic conditions.

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Last Updated: 09/08/2017
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Atypical nevus syndrome in Adult
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Atypical nevus syndrome : Scattered many, Widespread
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