Atypical dermal nodules in benign melanocytic naevi

The prognosis of deeply invasive melanoma can be poor and to a large extent it is unresponsive to treatment once metastases have occurred. It is therefore important that any dermal melanocytic lesions that have some features suggestive of melanoma but are nevertheless benign, should be identified.

A series of 40 benign melanocytic naevi is described in which the clinical presenting feature was a central focus of increased pigmentation. This was found histologically to correspond to dermal nodules of large melanocytes showing some, usually mild, nuclear atypia but low indices of cellular proliferation. The nodules are found within otherwise typical melanocytic naevi. The clinical and histological differential diagnosis included invasive melanoma but in follow-up, which is admittedly short (mean 24 months), none have recurred or metastasized.

It is suggested that the nodules represent terminal differentiation of melanocytes rather than proliferative changes. They should be distinguished from melanoma and regarded as a variant of benign melanocytic naevi.