Desmoplastic (sclerotic) nevus - An underrecognized entity that resembles dermatofibroma and desmoplastic melanoma

Desmoplastic (sclerotic) nevus, a benign melanocytic neoplasm characterized by predominantly spindle-shaped nevus cells within a fibrotic stroma, can be confused with fibrous lesions and other melanocytic proliferations, incl uding desmoplastic melanoma. We compared the histologic and immunohistochem ical features of 16 desmoplastic nevi, nine desmoplastic melanomas, four hy popigmented blue nevi, and six dermatofibromas. The similarities between de smoplastic nevi and dermatofibromas included epidermal hyperplasia(12 of 16 ), presence of keloidal collagen (15 of 16), hypercellularity (16 of 16), a nd increased numbers of factor XIIIa-positive dendritic cells (12 of 12). T he absence of adnexal induction (0 of 16), the rarity of lesions with multi nucleated cells (3 of 16) or epidermal hyperpigmentation (12 of 16), and th e presence of S-100 immunoreactivity (16 of 16) and melanocytic proliferati on (9 of 16) helped differentiate desmoplastic nevi from dermatofibromas, T he similarities between desmoplastic nevi and desmoplastic melanomas includ ed the presence of atypical cells (16 of 16) and HMB-45 expression in the s uperficial portion of the lesions (11 of 16). The infrequent location on th e head or neck (1 of 16), the absence of mitotic figures (0 of 16), a signi ficantly lower number of Ki-67-reactive cells, and a decrease in HMB-45 exp ression in the deep area of the lesions (8 of 11) helped distinguish desmop lastic nevi from desmoplastic melanoma. Desmoplastic nevi had overlapping f eatures with hypopigmented blue nevi, but features tending to favor the lat ter included a predominance of ovoid nuclei, higher numbers of atypical cel ls, and homogeneous staining with HMB-45. We conclude that a combination of histologic and immunohistochemical criteria facilitates the reliable diagn osis of desmoplastic nevus from its simulators.