Prediction of histologic melanocytic dysplasia from clinical observation

The dysplastic melanocytic nevus (DMN) is a putative precursor for malignant melanoma in persons with a family history of melanoma and multiple large atypical moles. Furthermore, the concept that DMN confers increased risk for melanoma has been extended to those without a family history of melanoma. Some investigators have characterized DMN in terms of size, surface topography, and irregularity of border and color and have provided definitive statements as to major and minor clinical "criteria" for DMN.

In this study we conducted a quantitative test of previously described clinical characteristics in patients diagnosed with melanoma but without a family history of melanoma in a first-degree relative (N = 153).

Two of us examined each patient independently, counting the total number of nevi, deciding on the most clinically atypical nevus, and recording quantitatively the size, surface, border, and color characteristics. The most atypical nevus was removed from each patient and diagnosed histologically without knowledge of the clinical examiner's description.

Of the 153 nevi so examined, 91 (59.5%) were judged to be clinically atypical and 23 nevi (15%) were classified as histologically dysplastic. We then analyzed the ability of each clinical feature to predict histologic melanocytic dysplasia. A multivariate analysis was conducted with the blindly scored clinical features as independent variables. Independent variables included total number of nevi and freckles as well as the features of the particular nevus biopsied (including longest diameter, macular component, irregular border, ill-defined border, haphazard coloration). Of the many independent clinical variables, only total number of nevi and macular component were useful in the final multivariate prediction. Of 21 nevi with a macular component removed from persons with more than 24 total body nevi, 7 were histologically dysplastic, representing a positive predictive value of 33.3% (95% exact confidence limits 14.6% to 57.0%). Of the 38 nevi without a macular component to their most atypical nevus removed from patients with 12 or fewer total body nevi, 37 failed to meet histologic criteria for DMN, representing a negative predictive value of 97% (95% exact confidence limits 86.2% to 99.9%).

We conclude that in nonfamilial melanoma, clinical criteria suggesting DMN when present will often fail to display histologic melanocytic dysplasia. In contrast, absence of a macular component in melanocytic nevi in a person with fewer than 13 total body nevi will accurately predict the absence of melanocytic dysplasia on histologic examination.