**2. Dermoscopy**

Dermoscopy of the nail unit is a noninvasive method that can help identify highrisk features.

Dermoscopy is useful to distinguish blood; subungual hemorrhage has a distinctive pattern of globules with distal streaks, a filamentous end, and red to brown or deep purple color. It is important to consider a bleeding tumor and rule out that possibility [5].

#### **Figure 3.**

*Dermoscopy of SUM in situ. Irregular multiple heterogenous brown bands with blurred edges and microhutchinson's sign.*

Subungual melanoma should be suspected and ruled out in heterogeneous longitudinal brown or black melanonychias, when bands are irregular in color, thickness, and spacing. SUM can also present as a diffuse dark background with barely visible lines (**Figure 3**). When a brown coloration in the background is overlaid by regular, parallel, and pigmented lines, the most probable diagnosis is a nevus.

Edge blurring is another sign associated with SUM. Hutchinson's sign is considered an indicator of SUM; however, it can also be found in benign nevi. Atypical Hutchinson's sign in SUM is asymmetric and polychromatic, and the pigment is distributed in a disorderly fashion. Micro-Hutchinson's sign is periungual pigmentation invisible to the naked eye and only observed with dermoscopy; it has only been described in SUM. Triangular shape of the longitudinal band (wider proximally than distally) indicates rapid growth [5, 6].

A grayish longitudinal background either alone or overlaid by thin homogenous gray lines is suggestive of melanocytic hyperplasia as in lentigo or lentiginoses (Laugier-Hunziker syndrome, Leopard syndrome, Peutz-Jeghers-Touraine disease), in drug-induced, ethnic, and traumatic nail pigmentation.

Amelanotic SUM is a very difficult diagnosis; in this rare case, the nail plate is often partially destroyed by a bleeding, erythematous vegetating tumor. Dermoscopy can show areas of remanant pigmentation and vascular disorder: irregular vessels and milky-red areas [5].
