Melanocytic nevi with nonsurgical trauma: a histopathologic study.

There is a belief among dermatopathologists that benign melanocytic nevi (BMN) may display atypical histologic characteristics when traumatized. However, to our knowledge, a systematic study of nonsurgically traumatized melanocytic nevi (TMN) has not been published. We studied a series of 92 TMN. Cases were analyzed for histologic evidence of architectural and cytologic criteria associated with atypia. Of the patients, 54 were female and 37 were male. The mean age was 38 years old (range 8-74 years old). Nevi were present, in order of frequency, on the extremities, trunk, and head/neck, but there were no acral sites. Histologic findings of trauma were as follows: parakeratosis (92%), dermal telangiectasias (61%), ulceration (51%), dermal inflammation (49%), melanin within stratum corneum (24%), and dermal fibrosis (25%). Pagetoid spread of melanocytes was limited to the site of trauma in 20% of cases and was identified away from areas of trauma in 8% of cases. Melanocytic atypia was seen in three cases. Dermal mitoses were rare (one mitotic figure in three cases). Pagetoid spread under a traumatized epidermis was relatively frequent and, in isolation, is compatible with a benign TMN. Any traumatized melanocytic lesion that displays cytologic atypia, pagetoid spread outside of the area of the traumatized epidermis, or dermal mitoses should be treated with caution because these findings were rarely seen in TMN.