Atypical Mole (Clark Nevus or Dysplastic Nevus) Workup

Updated: Feb 28, 2022
  • Author: Manuel Valdebran, MD; Chief Editor: Dirk M Elston, MD  more...
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Imaging Studies

Dermoscopy (epiluminescence microscopy) can be used to evaluate atypically pigmented lesions. In trained individuals, dermoscopy can improve accuracy in identifying melanoma from atypical nevi. [51] See Dermoscopy for more information.

In retrospective studies, total body photography has been shown to aid in detection of evolving melanomas and encourage patients to do self-skin examinations. This is expensive, requires special equipment and training, and may best be used in a pigmented lesion clinic. [35]

In 2012, in vivo confocal microscopy was used to identify a dysplastic nevus; pilot studies have shown significant reflectance confocal microscopy correlates. Some of the features identified were the presence of a ringed pattern, a meshwork pattern, atypical junctional cells in the center of the lesion, and irregular junctional nests with short interconnections. [52]

Multiphoton microscopy is a laser-scanning microscope that is able to provide assessment of Clark nevi. Although it is in its early stages of development, it promises to be a useful instrument to provide in vivo evaluation of these lesions. [53]


Histologic Findings

Typical histopathologic features, which are superimposed on those of a typical junctional or compound nevus, include the following (Note: Some clinical atypical moles are normal histologically):

  • An increased number of single melanocytes along the basal layer, with elongation of rete ridges

  • Cytologic atypia of melanocytes with enlarged, hyperchromatic nuclei in the junctional component: Atypia is usually confined to the shoulder region of the nevus. Diffuse atypia is more worrisome.

  • A horizontal arrangement of melanocytes, which generally vary in shape from round to spindled, although an occasional epithelioid configuration may also be identified

  • A tendency for melanocytes to aggregate into variably sized nests, which fuse with adjacent rete ridges to produce bridging

  • The presence of lamellar and concentric dermal fibroplasia [54]

  • The presence of a lymphocytic infiltrate (patchy or diffuse) in the superficial dermis

  • Extension of the junctional component many rete ridges beyond the last dermal nest to produce "shoulders"

The above changes may appear focally in any given lesion, and they may not be evident unless multiple histopathologic sections are studied.

The World Health Organization Melanoma Program has proposed a similar list of characteristics/criteria for dysplastic nevi. Criteria are divided into 2 major and 4 minor criteria. An individual lesion requires 2 major and 2 minor criteria to be classified as a dysplastic nevus. [11] Currently, most dermatopathologists are not using this classification scheme. However, the establishment of widely accepted criteria may eventually result in the uniform selection of patients for trials and population studies.

Human leukocyte antigen (HLA) expression may be useful as an objective biomarker of atypical nevi. In one study, HLA class I heavy chain, β2m, and HLA class II β chain were expressed in 8.6% of common nevi, compared with approximately 72% of atypical melanocytic lesions. The level of HLA expression was correlated with the degree of cytological atypia and architectural disorder in dysplastic lesions. [55]

Valdebran et al elucidate useful nuclear features for distinguishing atypical moles from melanoma. Specifically, atypical nevi more commonly have less prominent or absent nucleoli than do melanoma. Also, melanoma have a significantly greater frequency of the following nuclear features compared to atypical nevi:

  • Peppered moth nuclear pattern

  • Notching

  • Mitotic figures

  • Pleomorphism

  • Flattened adjacent nuclei

  • Vesicular nucleus with rounded nucleoli

  • Multiple nuclei [56]