**1. Introduction**

Subungual melanoma (SUM) is a subtype of acral lentiginous melanoma. It is a rare subtype in Caucasians accounting for 3% of all melanomas. In dark phototypes, Hispanics and Asians, it represents 20%, and it is the most frequent malignancy of the nail unit [1].

SUM or nail melanoma arises from dormant melanocytes in the nail unit, mainly in the nail matrix, and exceptionally in the nail bed.

UV radiation is not considered an important risk factor for this subtype of melanoma. Trauma has been a hypothetical etiologic agent. Many patients associate direct trauma to the onset of this malignancy, and it has been hypothesized that inflammation can cause mutations in melanocytes during trauma-induced proliferation; but a direct association has not been proven, and it may only be a coincidence due to increased attention to a longitudinal melanonychia after trauma [2].

SUM has a long radial growth phase that can last for many years; in this stage it presents as longitudinal melanonychia, and the differential diagnosis includes racial and traumatic melanocytic activation, nail matrix nevi, and lentigo of the nail unit [3].

Nail plate pigmentation can also be caused by blood and external pigments such as silver in argyria. Many drugs cause nail pigmentation by drug deposition or by melanocytic activation (minocycline, psoralens, cyclophosphamide, zidovudine). Bacterial or fungal infections (*Proteus mirabilis*, *Aspergillus* sp., *Candida* sp., *Trichophyton rubrum*) can cause nail pigmentation; other subungual tumors such as epidermoid carcinoma and even a subungual wart can present as longitudinal melanonychia [3].

Clues to the diagnosis of melanoma include a single-digit affection, melanonychia wider than 3 mm with a triangular form (this means that the band is growing), rapid widening of a longitudinal melanonychia, onset in adulthood (melanoma in children is quite rare), and Hutchinson's and micro-Hutchinson's sign [4] (**Figure 1** and **Table 1**).

In more advanced stages, SUM causes nail dystrophy, ridging, partial destruction of the nail plate, ulceration, bleeding, and total destruction of the nail unit (**Figure 2**).

SUM affects women and men equally, although some series report a slight predominance in women. SUM is more common on the dominant hand, and it is more frequently reported on the thumbs and on the first finger on both toes [1].

#### **Figure 1.**

*SUM in situ. Longitudinal irregular melanonychia with nail plate ridging.*


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**Figure 3.**

*microhutchinson's sign.*

*Subungual Melanoma*

**2. Dermoscopy**

risk features.

**Figure 2.**

possibility [5].

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

SUM is frequently diagnosed in advanced stages, due to a delay in diagnosis by healthcare providers not aware of its existence and clinical presentation or due to lack of access to medical services. The median Breslow at diagnosis is between 4 and 6 mm [1].

*Invasive SUM with Hutchinson's sign and partial destruction of the nail plate.*

Dermoscopy of the nail unit is a noninvasive method that can help identify high-

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

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

**Table 1.** *ABC rule to suspect SUM.*

*Cutaneous Melanoma*

sign [4] (**Figure 1** and **Table 1**).

(melanoma in children is quite rare), and Hutchinson's and micro-Hutchinson's

frequently reported on the thumbs and on the first finger on both toes [1].

A Age: 40–60 years. Does not rule out in children African, American, Asian, Hispanics

*SUM in situ. Longitudinal irregular melanonychia with nail plate ridging.*

No change: failure to improve

Thumb-hallux-index finger

Nail dystrophy: ridging ulceration E Extension—Hutchinson's sign: pigment on nail folds

Micro-Hutchinson: cuticle pigmentation visible with dermoscopy

Dominant hand

F Family or personal history of melanoma

B Band: brown-black irregular Blurred borders >4 mm C Change: rapid increase in size

D Single digit:

**Table 1.** *ABC rule to suspect SUM.*

In more advanced stages, SUM causes nail dystrophy, ridging, partial destruction of the nail plate, ulceration, bleeding, and total destruction of the nail unit (**Figure 2**). SUM affects women and men equally, although some series report a slight predominance in women. SUM is more common on the dominant hand, and it is more

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*Adapted from [4].*

**Figure 1.**

**Figure 2.** *Invasive SUM with Hutchinson's sign and partial destruction of the nail plate.*

SUM is frequently diagnosed in advanced stages, due to a delay in diagnosis by healthcare providers not aware of its existence and clinical presentation or due to lack of access to medical services. The median Breslow at diagnosis is between 4 and 6 mm [1].
