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Context.-The diagnosis of recurrent nevus poses a potential challenge to practicing pathologists. Although most recurrent nevi show uniform microscopic findings and pose no great diagnostic difficulty, a few cases exhibit some histopathologic features similar to, and in some cases indistinguishable from, melanoma. Historically, the term pseudomelanoma has been used in the literature to describe such recurrent nevi, although this label has the potential for confusion and is no longer the favored term for recurrent pigmented melanocytic nevi.
Objective.-To describe historical, histopathologic, and immunohistochemical features of recurrent pigmented melanocytic nevi and to review briefly the literature surrounding the mechanism of recurrence.
Data Sources.-Published peer-reviewed literature and the authors' personal experience.
Conclusions.-Recognition of the histopathologic pattern of recurrent nevi leads the pathologist to the correct diagnosis in most cases; however, in particularly challenging specimens or in circumstances in which there is insufficient clinical history, immunohistochemical studies have proved helpful in distinguishing recurrent nevi from melanoma.
(Arch Pathol Lab Med. 2011;135:842-846)
EARLY STUDIES
Some dermatologists in the 1950s held the disturbing opinion that partial removal of melanocytic nevi, particularly when performed by electrodesiccation, might induce the nevic remnant to change into a melanoma; however, no published studies proved that such malignant transformation occurred. To address this topic, Walton et al1 examined 112 biopsy specimens of pigmented nevi from 75 patients that were removed by shave technique, followed by light electrodessication, and subsequently completely excised at intervals of from 3 to 12 months. This seminal report marked the beginning of what would henceforth become the challenging, often controversial, and ultimately edifying study of the recurrent nevus phenomenon.
In their study, Walton et al1 found no evidence of malignant change in either the original nevus (ON) or the recurrent nevus. The authors concluded that partially removed nevi, which later gave rise to melanoma, were more likely already to have been undergoing malignant change at the time of initial biopsy than to have been transformed by the biopsy process itself. Clinical recurrence of pigmentation at the biopsy site was reported to occur in more than half of subjects and, although of concern clinically, it was reported to represent the presence of pigmented nevus cells, with no signs of increased mitotic index.1 A subsequent study of 19 recurrent nevi (RN) similarly...