Abstract

Perineuriomatous melanocytic nevi were first described in 2011, and one small series (McAfee et al) has since been published. To better characterize this melanocytic tumor subtype, we reviewed the experience in a busy consultation practice. Twenty-seven cases were retrieved by computerized database search. Demographic and clinical information, including the clinical impression, were tabulated, and the histopathologic and immunoperoxidase findings were also scored. The tumors presented in patients aged 13-80 years (mean = 50 years). The clinical impression included dysplastic nevus, benign nevus, BCC, and NUB. Site of occurrence was widely distributed including arm (7), leg (6), trunk (10), ear (2), and forehead/scalp (2). Histopathologically, all tumors included a mix of conventional nested melanocytic differentiation and spindled nerve sheath differentiation. Twenty tumors (74%) exhibited interstitial EMA positivity. Expression of p16 was retained, and PRAME expression was not identified. One tumor was of Spitz lineage, and one was exophytic and polypoid. One exception tumor exhibited marked myxoid stromal change in the nerve sheath component. More than 50% of cases raised diagnostic concern for desmoplastic melanoma in the differential diagnosis of the contributor. Our data suggest that perineuriomatous melanocytic nevi remain unfamiliar and diagnostically challenging. Perineuriomatous differentiation can be found in melanocytic nevi of both conventional and Spitz lineage. Dramatic myxoid change can occasionally be observed.