[Desmoplastic Spitz nevus: a histopathological review and comparison with desmoplastic melanoma]

Abstract

Introduction: Desmoplastic Spitz nevus is a rare variant of spitzoid tumours characterized by dermal proliferation of large epitheliod and/or fusiform melanocytes within a desmoplastic stroma, comprising thick, eosinophilic collagen bundles. It occurs most frequently in young adults and children, and exhibits a predilection for the limbs. Histologically, this entity may be mistaken for cutaneous fibrous tumours or desmoplastic melanoma. To establish useful histological criteria for differential diagnosis of desmoplastic Spitz nevus, we conducted a retrospective study comparing data concerning the clinical, demographic and histological characteristics of desmoplastic Spitz nevus and desmoplastic melanoma.

Patients and methods: We reviewed the slides for 28 cases of desmoplastic Spitz nevus and for 13 cases of desmoplastic melanoma obtained from the files of Pinkus Dermatopathology Laboratory (Monroe, MI, USA) during the period 1993-2005.

Results: Desmoplastic Spitz nevus was more common in women (sex ratio M/F=0.4) and younger patients (mean age: 28.2 years) whereas the mean age of patients with desmoplastic melanoma was significantly higher (mean age: 75 years). From a histopathological point of view, symmetry, circumscription, melanocytic maturation and involvement of adnexal structure were significantly more frequent in desmoplastic Spitz nevi. The presence of melanocytic junctional nests associated with discohesive cells, variations in size and shape of the nests, lentiginous melanocytic proliferation, actinic elastosis, pagetoid spread, dermal mitosis, perineural involvement and brisk inflammatory infiltrate were significantly more frequent in desmoplastic melanoma. No significant difference was found concerning epidermal hyperplasia, presence of Kamino bodies or moderate inflammatory infiltrate.

Conclusion: The combination of architectural and cytological features was useful in differentiating desmoplastic Spitz nevus from desmoplastic melanoma. A complete excision biopsy is mandatory in such tumors as the architectural criteria are necessary for a correct diagnosis.