Abstract:

Melanocytic nevi with neural features are uncommon and diagnostically challenging lesions on histology. “Neurotized” nevi can be difficult to distinguish from neurofibroma variants, melanoma, or even neuromas in the setting of recurrent trauma. Immunohistochemical studies, particularly S100 and Melan-A, have been described as useful methods for differentiating these entities; however, unusual staining patterns can complicate the diagnosis. A 36-year-old, active duty military male presented with an exophytic, skin-colored papule on the central back present for 30 years that enlarged and became irritated over several weeks while wearing military-issued gear. A shave biopsy of the lesion revealed a densely cellular dermis with loosely arranged nests of cytologically unremarkable melanocytes and intervening fibrosis. A second population of epithelioid to spindled cells arranged in tight fascicles with associated mast cells was identified distant to the melanocytic nests. The fascicular population demonstrated diffuse, strong S100 positivity and blush positivity for neuron specific enolase (NSE), which suggested a neural staining pattern. Melan-A, MiTF, and tyrosinase staining was positive in the melanocytic nests but negative in the fascicular component. However, SOX10 staining was strongly positive in both the nested and fascicular components of the lesion. This case was therefore consistent with a benign intradermal nevus with neural features displaying aberrant loss of several common melanocytic markers in neurotized melanocytes. As demonstrated in this case, it is valuable to recognize the potential for unusual immunohistochemical features in neurotized nevi to more efficiently and accurately diagnose these relatively rare, benign neoplasms.

Financial Disclosure:
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