Spitz nevi are acquired nevi that occur most commonly in children. The classic Spitz nevus is a benign growth with minimal malignant potential. The Spitz nevus is also known as a spindle-cell nevus. In the past, they were also referred to as “benign juvenile melanoma,” but that name should be avoided, because the term melanoma should be used to describe malignant tumors only. The difficulty with these melanocytic growths is that they do not always have the classic appearance and can be difficult to differentiate from melanoma. This is especially true in the adult population, where Spitz nevi are uncommon. For this reason, the terms atypical Spitzoid melanocytic lesion, atypical Spitz nevus, and Spitzoid tumor of undetermined potential have made their way into the dermatology lexicon to describe these difficult-to-classify cases.
Clinical Findings: The classic Spitz nevus occurs in childhood and has a characteristic reddish-brown color. It has even coloration and regular borders. It is typically dome shaped and smooth. It occurs equally in boys and girls and is more commonly found in the Caucasian population. The most common location has been reported to be the lower limb. The size is variable, but they are usually 5 to 10 mm in diameter. Spitz nevi are almost always solitary, but multiple Spitz nevi in an agminated pattern have been described. The clinical differential diagnosis of a Spitz nevus includes the common acquired nevus, pilomatricoma, dermatofibroma, adnexal tumors, and juvenile xanthogranuloma. Most Spitz nevi are asymptomatic and are brought to the clinician’s attention as an incidental finding. Classic Spitz nevi rarely, if ever, spontaneously bleed or change in color.
Pathogenesis: The Spitz nevus is a melanocytic lesion derived from spindle-shaped or epithelioid melanocytes. The initiating factor or factors that cause this melanocytic proliferation to arise are unknown. They are unique melanocytic lesions, and their pathogenesis is likely to be entirely different from that of congenital melanocytic or common acquired melanocytic nevi.
Histology: The classic Spitz nevus is symmetrically shaped, without shouldering. It shows the proper benign maturation of melanocytes from top to bottom of the lesion. The melanocytes do not show pagetoid spread (single melanocytes) within the epidermis. Spitz nevi melanocytes in general have a spindle shape or epithelioid morphology. Another helpful finding is the presence of eosinophilic Kamino bodies. These can be either solitary or coalescing into large globules. Kamino bodies are found in juxtaposition to the basement membrane zone and are composed of elements of the basement membrane, specifically type IV collagen. There is no immunohistochemical stain that can definitively differentiate a Spitz nevus from melanoma. As alluded to earlier, the classic Spitz nevus is usually a straightforward diagnosis. However, many difficult-to-classify melanocytic lesions have overlapping features of Spitz nevus and melanoma and can be exceedingly challenging diagnostically.
Treatment: Complete excision for a classic Spitz nevus is curative and allows for a complete histological evaluation. Indeterminate lesions should be reexcised with conservative margins to make sure they have been completely removed. Spitz nevi in adults should all be excised to allow for complete histopathological examination. Unclassifiable or difficult to classify melanocytic tumors with features of both Spitz nevus and melanoma are best treated as if they were melanoma. The Breslow depth should be used to plan for appropriate therapy.