**3. Nail matrix biopsy**

Nail matrix biopsy remains essential for diagnosis. Most melanomas arise from the distal matrix; by performing dermoscopy of the free edge of the nail plate, it is sometimes possible to determine the origin of melanonychia. If the distal matrix is the origin of melanonychia, the ventral aspect of the nail plate will be affected, and if the proximal nail matrix is the origin, the dorsal aspect of the nail plate will be pigmented.

**71**

*Subungual Melanoma*

**Figure 5.**

*Lateral longitudinal nail biopsy.*

*DOI: http://dx.doi.org/10.5772/intechopen.85450*

and report Breslow depth (**Figure 5**).

**4. Histology**

matrix epithelium) [7].

The surgical technique consists in exposing the nail matrix, identifying the origin of melanonychia, and taking a representative sample of the nail matrix without leaving permanent nail dystrophy. This technique is performed under digital block anesthesia. First, the nail plate has to be removed, and a flap of the proximal nail fold elevated so that the proximal and distal nail matrix is exposed (**Figure 4**). Intraoperative dermoscopy of the nail matrix is an effective tool to precisely identify the origin of the pigment. A longitudinal matrix biopsy, no more than 3-mm-wide or a 3-mm-punch biopsy, can be done without risk of dystrophy; a shave biopsy of the matrix 1 mm deep is enough to make the diagnosis and lessens the risk of permanent dystrophy. There is no need to suture the nail matrix; the nail plate and the proximal nail fold are relocated and sutured with a 4-0 nonabsorbable suture. In cases of invasive SUM, a lateral longitudinal nail biopsy that includes the proximal fold, the matrix lateral horn, the nail bed, the plate, and the distal nail fold is easier to perform and gives the pathologist enough tissue to make the diagnosis

Nail matrix biopsy is still essential for SUM diagnosis. Normal nail matrix has between 4 and 14 melanocytes per mm (mean 6.86 cells/mm per mm stretch of nail

The presence of nests without atypia is distinctive of nevi, especially in a child

The histologic distinction between a benign subungual pigmented macule (lentigo or lentigo-like hyperpigmentation) and an early lesion of SUM can be difficult. This benign lentigos may histologically only show an increase in melanin deposition in keratinocytes, melanocytes, and/or macrophages without proliferation of melanocytes (melanocytic activation). However, these benign lesions may show proliferation of melanocytes as well. The mean density of melanocytes in lentigos is around 15.3 cells per 1-mm-stretch nail matrix. There is no confluence of melanocytes. Cytologic atypia has to be absent or mild. There is no inflammation

SUM in situ shows a much greater proliferation of melanocytes (mean 58.9 cells per 1 mm of stretched nail matrix) that ranges from 39 to 136 melanocytes per 1 mm of stretched nail matrix. There is at least focal confluence of cells with various grades of cytologic atypia: nuclear enlargement, hyperchromatism, irregular nuclear contours, and prominent nucleolus. Dendrites are thicker and larger. Pagetoid spread is found in almost all lesions of SUM, and inflammation in the

with a well-demarcated, uniformly pigmented, single, longitudinal band [8].

associated. Pagetoid spread may be present but only focally.

**Figure 4.** *Nail matrix biopsy technique: proximal nail fold flap and exposure of the nail matrix.*

**Figure 5.** *Lateral longitudinal nail biopsy.*

*Cutaneous Melanoma*

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,

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 proxi-

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),

is often partially destroyed by a bleeding, erythematous vegetating tumor. Dermoscopy can show areas of remanant pigmentation and vascular disorder:

*Nail matrix biopsy technique: proximal nail fold flap and exposure of the nail matrix.*

Amelanotic SUM is a very difficult diagnosis; in this rare case, the nail plate

Nail matrix biopsy remains essential for diagnosis. Most melanomas arise from the distal matrix; by performing dermoscopy of the free edge of the nail plate, it is sometimes possible to determine the origin of melanonychia. If the distal matrix is the origin of melanonychia, the ventral aspect of the nail plate will be affected, and if the proximal nail matrix is the origin, the dorsal aspect of the nail plate will be pigmented.

parallel, and pigmented lines, the most probable diagnosis is a nevus.

mally than distally) indicates rapid growth [5, 6].

irregular vessels and milky-red areas [5].

**3. Nail matrix biopsy**

in drug-induced, ethnic, and traumatic nail pigmentation.

**70**

**Figure 4.**

The surgical technique consists in exposing the nail matrix, identifying the origin of melanonychia, and taking a representative sample of the nail matrix without leaving permanent nail dystrophy. This technique is performed under digital block anesthesia. First, the nail plate has to be removed, and a flap of the proximal nail fold elevated so that the proximal and distal nail matrix is exposed (**Figure 4**).

Intraoperative dermoscopy of the nail matrix is an effective tool to precisely identify the origin of the pigment. A longitudinal matrix biopsy, no more than 3-mm-wide or a 3-mm-punch biopsy, can be done without risk of dystrophy; a shave biopsy of the matrix 1 mm deep is enough to make the diagnosis and lessens the risk of permanent dystrophy. There is no need to suture the nail matrix; the nail plate and the proximal nail fold are relocated and sutured with a 4-0 nonabsorbable suture.

In cases of invasive SUM, a lateral longitudinal nail biopsy that includes the proximal fold, the matrix lateral horn, the nail bed, the plate, and the distal nail fold is easier to perform and gives the pathologist enough tissue to make the diagnosis and report Breslow depth (**Figure 5**).
