Short Brown Parallel Lines on the Proximal Nail Fold. Clinical-Dermoscopic-Histologic Correlation of a Melanocytic Nevus of the Eponychium.

Introduction: Although Hutchinson's sign can appear associated with benign conditions, dermoscopic findings of non-melanoma eponychium pigmentation have not yet been described in the literature. We report for the first time to our knowledge the dermoscopic findings of an acral nevus located in the proximal nail fold as well as its clinical-dermoscopic-histologic correlation.

Case Report: A twenty-year-old patient presented with a homogeneous longitudinal melanonychia on the left-hand thumb, with benign dermoscopic pattern, and an irregular, 6-mm, dark-brown hyperpigmented macule on the adjacent eponychium (Hutchinson's sign). The eponychium lesion showed on dermoscopy two irregular brown-black pigmented blotches, with superimposed parallel brown lines on a brushy distribution, with a thicker terminal end. The histopathologic examination of the proximal nail fold was performed, revealing scattered nevus cells in the epidermal basal layer and dermal-epidermal junction thecae, without any atypia or mitosis. These features were consistent with nevus of the proximal nail fold.

Discussion: Previous descriptions of benign hyponychium's pigmentations, despite the malignant appearance of the overlying melanonychia, were reported to have a similar dermoscopic pattern, known as longitudinal brushy pigmentation. This newly described dermoscopic sign on the eponychium may help distinguish Hutchinson's sign related to subungual melanoma to non-melanoma Hutchinson's sign.