The efficacy of histopathological criteria required for diagnosing dysplastic naevi.

The efficacy of specific histopathological features for diagnosing dysplastic naevi was established by comparing their frequency in 62 dysplastic naevi, from 36 patients with the dysplastic naevus syndrome, with those in 326 ostensibly benign naevocellular naevi derived from a group of 67 autopsy cases. Individual diagnostic features had a low sensitivity, a low specificity or low predictive values. Discriminant analysis showed that the presence of dust-like melanin, irregular naevoid nests, markedly increased junctional activity and melanocytic nuclei equal or larger in size than overlying keratinocyte nuclei were the most discriminating features. Using two or more of these criteria plus a lymphocytic infiltrate as an obligatory diagnostic criterion, a reasonable efficacy could be reached for dysplastic naevi. Based on these combinations of criteria the prevalence of histologically proven dysplastic naevi in the autopsy group would be 10%. Lesions with all these four discriminating features were found in half of the patients from the dysplastic naevus syndrome group, but were absent in the autopsy group. We suggest that such severely atypical dysplastic naevi may be indicative of patients at high risk for developing malignant melanoma.