LAUSR

Acral lentiginous melanoma accounts for less than 5% of all melanomas, and most often appears on palmar, plantar, subungual, and mucosal surfaces (Wolff, Goldsmith, Katz, Gilchrest, Paller, Leffell, 2008). Subungual melanoma (SM) is a rare type of acral lentiginous melanoma that represents only 0.7–3.5% of reported melanoma cases (Levit, Kagen, Scher, Grossman, & Altman, 2000). SM is often misdiagnosed and improperly treated as various benign conditions including onychomycosis, pigmented nevus, as well as drug induced or malnutrition induced hyperpigmentation. Therefore, most SMs are in advanced stages at the time of diagnosis, therefore, associated with a poor prognosis (Cochran, Buchanan, Bueno, & Neumeister, 2014). Early stage of SM is often difficult to differentiate from benign melanocytic lesions. However, making the correct diagnosis is crucial, as treatment and prognosis of these two entities significantly differ. Typically, SM initially present as melanonychia striata, often followed by development of the Hutchinson sign, which is the most significant clinical sign in differentiating SM from benign melanocytic lesions. In situ melanoma usually arises in the nail matrix, from where it can extend to the ventral part of the proximal nail fold or to the nail bed. Furthermore, in cases of in situ melanoma, single melanocytes predominate over nests in most fields, however rare small nests are occasionally present upon histopathologic evaluation. In these early lesions, the atypia is often focal and moderate, and displays pagetoid spread (Calonje, Brenn, & McKee, 2011).