[Focal melanocytic atypia in dysplastic nevus cell nevi. Results of a serial section study]

Dysplastic nevi were diagnosed according to the ABCDE rule for recognition of early melanomas in 11 patients with familial dysplastic nevus syndrome (DNS) and in 39 patients with the sporadic variant of DNS. All these 50 patients exhibited multiple dysplastic nevi. On routine histological examination melanocytic atypia confirming the histological diagnosis of dysplastic nevus was found only in 12/50 cases. However, when cut consecutively dysplastic nevi with melanocytic atypia were diagnosed in 17 further cases (34%). In most cases (72.4%) only a mild degree of atypia (grade I) was found. Dysplastic nevi with severe melanocytic atypia (grades II-III) were found in all groups of sporadic and familial variants of DNS (with and without melanoma). To improve the prognostic value of the histological examination in dysplastic nevi significantly it must be of interest to add the degree of melanocytic atypia. With increasing degree of melanocytic atypia also the typical histological feature of dysplastic nevi become more significant. Since such atypia in dysplastic nevi is not necessarily sited in the centre of the lesion and since in most cases melanocytic atypia occurs focally, we believe that histological examination of dysplastic nevi must be undertaken by step section. Lesions suspected of being dysplastic nevi must be excised with margins of at least 2-5 mm for a correct histological diagnosis.