Histological analysis of intraepidermal proliferations of atypical melanocytes

Fifty cutaneous pigmented lesions characterized by an intraepidermal proliferation of atypical melanocytes were reviewed. Several histological parameters (position of melanocytes in the epidermis, nuclear melanocytic atypia, presence or absence of pagetoid melanocytes, nucleoli, and others) were evaluated. On the basis of the results, the investigated cases were classified into three groups. In group 1, pagetoid melanocytes were present, melanocytic atypia was severe and continuous, all epidermal layers were involved by melanocytic proliferation, and a pattern of epidermal infiltration was recognized. In group 2, pagetoid melanocytes were absent, melanocytic atypia was mild-moderate and discontinuous, the lower epidermis only was involved by melanocytic proliferation, and a pattern of epidermal pseudoinfiltration was recognized. Group 3 cases were in an intermediate area between the two major groups. The results showed that intraepidermal proliferations of atypical melanocytes lie on one line, in which groups 1 and 2 account for the extremes.