Amelanotic melanoma of the nail unit: Clinical and dermoscopic features of the nail plate changes

Melanoma is a heterogeneous cancer consisting of different subsets. Nail melanoma (NM) represents a rare subtype, particularly in Caucasians. Its etiology, pathogenesis, and natural history remain poorly understood. In most cases, NM presents as a pigmented longitudinal band involving initially the nail plate and/or the nail folds. The clinical and dermoscopic features of these cases have been described in various series and new diagnostic algorithms have been proposed. ¹ , ² , ³ , ⁴ On the other hand, since the paucity of cases, very few are the descriptions for the amelanotic variant of NM.

We describe herein the clinical and dermoscopic features of a series of amelanotic cases of NM focusing on the evaluation of nail plate changes.

We retrospectively analyzed records of 2150 consecutive patients who had a histopathological diagnosis of melanoma and selected the nail apparatus location. We further selected cases that had undergone iconography between January 2007 and June 2019, at the Oncologic Dermatology Unit, IRCCS Azienda Sant'Orsola Malpighi Hospital.

Digital dermoscopic images were collected using a videodermatoscope (FotoFinder dermoscope, FotoFinder Systems GmbH, Bad Birnbach, Germany) with 20 and 40 magnifications.

Medical records and dermoscopic images of patients affected by NM were reviewed retrospectively by four dermatologists (E.D., S.V., P.A.F., and C.B.).

Demographic data regarding the clinical and dermoscopic presentation of NM were collected and analyzed based on Good Clinical Practice.

The study protocol was approved by the Local Research Ethic Committee, IRCCS Azienda Ospedaliera Universitaria Sant'Orsola‐Malpighi (Skin Cancer 18).

The endpoint of our study was to define the most frequent clinical and dermoscopic features of the nail plate and nail bed changes in amelanotic NM.

A total of 42 patients were diagnosed with NM from our records. All cases that presented pigmentation of nail plates or nail folds were excluded. Twelve cases (8 women, and 4 men) were recorded with a clinical diagnosis of amelanotic NM. Median age was 76.5 (range 45–89 years) (Table 1).

TABLE 1.

Demographic data of patients and NM clinical characteristics.

	Amelanotic NM (n = 12)
Sex
Male	4
Female	8
Age (years)
Median (range)	76.5 (45–89)
< 60	1
≥60	11
Localization
Hand	7
Foot	5
Histology
Nodular	11
Superficial spreading melanoma	1
Breslow thickness (mm)
Mean	3.9
T1: ≤1	1
T2: 1.01−2	3
T3: 2.01−4	3
T4: ≥4	5
Metastases
None	2
Local (lymph nodes/cutaneous)	2
Distant (visceral)	8

Abbreviation: NM, nail melanoma.

Regarding clinical features, a progressive thinning and fissuring of the nail plate starting from the proximal nail fold and the absence of the cuticle was observed in all cases (Figure 1). Three scenarios were annotated (1) nail plate deformity or changes involving less than 1/3 in width of the nail plate (one patient) (Figure 1B); (2) nail plate deformity or changes involving more than 1/3 of the nail plate (seven patients) (Figure 1A); and (3) total absence/atrophy of the nail plate associated with the presence of erosions or ulcerated or nodular masses (four patients) (Figure 1A). These latter masses appeared erythematous, sometimes with hemorrhagic spots or crusts.

FIGURE 1.

(A). and (B). Clinical images of amelanotic NM presenting with nail plate dystrophy. (C) and (D) Dermoscopy of the nail bed nodules: polymorphic vessels within pinkish areas. NM, nail melanoma.

On dermoscopy, polymorphic vessels (glomerular, hairpin, comma‐like, dotted, and linear vessels) surmounting red‐whitish structureless areas were observed (Figure 1C,D).

Dystrophic changes of the nail plate in the absence of pigmentation can be observed in association with other nail tumors, such as onychomatricoma, onychopapilloma, glomus tumor, digital cysts and squamous cell carcinoma (SCC). ⁵ , ⁶ , ⁷ , ⁸ , ⁹ However, some differences can be pointed out. For onychomatricoma, distal onycoscopy is pathognomonic in the observation of the honeycomb appearance of the nail plate. Similarly, in onicopapilloma nail plate changes occur in the distal edge and determine focal hyperkeratosis. The dimensions of the dystrophy associated with glomus tumors are usually smaller, unable to reach 1/3 of the nail plate width. For digital cysts, instead, it is important to monitor the dynamic changes occurring over time, because these lesions usually determine revocable dystrophic changes of the nail plate that may totally heal and further recur.

In nail SCC local hyperkeratosis of the nail plate is usually detected, ⁶ , ¹⁰ while when it presents as an invasive nodular variant a diagnostic biopsy is mandatory.

In our series most of the patients were elderly females and the main location was the first foot or hand digit. Similarly to the cutaneous counterpart amelanotic NM presented with an elevated Breslow thickness at the time of diagnosis. The prognosis was also poor: ten patients developed metastases dying in less than 3 years from the diagnosis; two patients are currently in follow‐up after 7 and 9 years from the diagnosis.

In conclusion, the amelanotic variant of NM can be often misdiagnosed even by trained specialists for the lack of pathognomonic features and symptomatology. Alteration of the nail plate toward progressive dystrophy in association with the presence of erosions or nodules of the nail bed should be sent for a prompt pathologic examination.

CONFLICT OF INTEREST STATEMENT

The authors have no conflict of interest to declare

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.