SPITZ NEVUS
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.
