Nail matrix melanoma: consecutive cases in a general practice

Nail matrix melanoma, otherwise known as subungual melanoma, is unique in that the actual primary cutaneous melanoma is occult, being covered by the nail plate and the proximal nail fold. Fortunately, the concealed melanoma may produce melanin, which then appears as longitudinal pigmentation in the nail plate. Thus melanin-producing nail matrix melanoma has a distinctive ‘signature’ to the informed observer. 
 
Acral lentiginous melanoma was first described as a subgroup in 1976 by Reed [1]. Prior to that Clark had proposed three histologic sub-types: superficial spreading melanoma, lentigo maligna melanoma and nodular melanoma [2]. About half of all hand and foot melanomas are of the acral lentiginous subtype. A Scottish study restricted to subungual melanoma showed that 45% were acral lentiginous, 27% nodular and 20% superficial spreading in type [3]. 
 
We present two consecutive cases of nail matrix melanoma from a general practice. The first patient was referred to the practice and the second patient was recommended to the practice by the first.


Introduction
Nail matrix melanoma, otherwise known as subungual melanoma, is unique in that the actual primary cutaneous melanoma is occult, being covered by the nail plate and the proximal nail fold. Fortunately, the concealed melanoma may produce melanin, which then appears as longitudinal pigmentation in the nail plate. Thus melanin-producing nail matrix melanoma has a distinctive 'signature' to the informed observer.
Acral lentiginous melanoma was first described as a subgroup in 1976 by Reed [1]. Prior to that Clark had proposed three histologic sub-types: superficial spreading melanoma, lentigo maligna melanoma and nodular melanoma [2].
About half of all hand and foot melanomas are of the acral lentiginous subtype. A Scottish study restricted to subungual melanoma showed that 45% were acral lentiginous, 27% nodular and 20% superficial spreading in type [3].
We present two consecutive cases of nail matrix melanoma from a general practice. The first patient was referred to the practice and the second patient was recommended to the practice by the first.

Case report 1
A 25-year-old high school science teacher was referred with a lesion on his right thumbnail ( Figure 1A), arriving by a circuitous route. One of his teenage students had seen a photograph of a nail melanoma on a patient education poster in the waiting room of a doctor's surgery office and thought the photo looked like her teacher's thumb. At first he was somewhat sceptical, but she persisted until he saw his GP, who referred him to a specialized melanoma centre. They, in turn, referred him to the general practice of author CR for a nail matrix biopsy because their preferred plastic surgeon had been temporarily incapacitated by an injury.

64
Observation | Dermatol Pract Concept 2012;2(2):13 The patient had first noticed a fine band of pigment extending the full length of the nail 10 months earlier that had become progressively wider since then.
Dermatoscopy of the surface of the nail plate ( Figure 1B) revealed longitudinal melanonychia (also known as melanonychia striata) with lines parallel stretching from the proximal nail fold to the free edge of the nail. The parallel lines varied in width, colour (black, dark brown, light brown and gray) and interval. The pigmented band was wider proximally than distally, consistent with a growing lesion in the nail matrix.
Braun et al [4] have demonstrated how dermatoscopy of the free edge of the nail plate can be used to precisely predict tumour location in the nail matrix. Pigment located deeply in the nail plate ( Figure 2) corresponds to a tumour located in the distal nail matrix.
A provisional diagnosis of nail matrix melanoma was supported by both the history of a new and progressively    Histopathology ( Figure 11) revealed (quoting from the pathology report) "a mild increase in basal melanocytes." The pathologist went on to state, "As usual in matrix preparations it is almost impossible to detect any atypia . . . I am performing a battery of four melanocytic markers in an attempt to clarify the pathology." Immunostaining was performed ( Figure 12) and the follow-up report stated, "Three of the immunoperoxidase  The patient was referred to a plastic surgeon for definitive treatment of a level 1 nail matrix melanoma.

Discussion
Durbec et al performed a comprehensive literature review of the epidemiology of hand and foot melanoma (HFM) [5].
They conclude that HFM is rare in all populations, with estimates of incidence of HFM ranging from 0.04 to 0.25 per 100,000 per year. They found one study, which specifically addressed the incidence of (invasive) subungual melanoma, with a finding of 0.1 per 100,000 per year (1 in a million per year) [6]. For HFM in general, ultraviolet radiation appears to have, at most, a very limited causative role, with previous trauma and nevi on the soles or toes being the most consistent risk factors across the few relevant studies. In one study nail trauma was recalled by 50% of patients with subungual melanoma [7]. Subungual melanomas were evenly distributed between hand and foot, but hallux and thumbnails were disproportionately affected compared to other digits and there was equal incidence of nail subungual melanoma across all races.
HFM appears to have a worse prognosis than cutaneous melanoma in general. This is thought to be mainly due to shown to assist in differentiating early nail matrix melanoma from other causes of nail pigmentation [8]. In Case 1 these features were clearly present, but in Case 2 they were equivocal. Another described clue to subungual melanoma is onset of longitudinal melanonychia during adulthood [8], and taking this into account, along with equivocal dermatoscopic features, a nail matrix biopsy was appropriate in Case 2.
A method known as the ABCDEF rule has been proposed to assist with early diagnosis of subungual melanoma [9].
In this method the letters have the following relevance: A) Age-peak incidence fifth to seventh decades with Africans, Furthermore, the differentiation between melanocytes and keratinocytes can be difficult with H&E stained specimens.
In both of the cases reported here immunoperoxidase stains were performed to facilitate a confident diagnosis.
Braun et al [7] describe a full range of biopsy techniques suitable for longitudinal melanonychia of varying sizes and locations. The biopsy technique used for these two cases is a modification of the punch method, with the fenestrated portion of nail plate being submitted for histology rather than being placed back into the defect as a "biological dressing." In both these cases healing proceeded rapidly without replacing the nail plug.
While invasive nail matrix melanomas are inevitably treated by partial or complete amputation of the affected digit according to tumour thickness, in-situ nail matrix melanomas can be treated by conservative excision of the entire nail apparatus (nail plate, bed and matrix) with graft reconstruction [7,10]. As even partial loss of thumb or big toe causes significant disability, diagnosis at the in-situ stage has led to a better functional outcome, as well as a better prognosis for these two patients.

Conclusion
An uncommon, occult form of melanoma was diagnosed at an early stage in two young adults because an informed teen-chaotic (chaos being defined as asymmetry of structure or colour). Therefore, lines parallel, varying in width, interval and colour, stretching the full length of a nail should lead to consideration of appropriate biopsy. Longitudinal nail pigmentation not fulfilling these criteria; and with a history of worrying features, such as recent onset or change, could be further assessed by sequential digital photographic monitoring with any increase in bandwidth or band chaos leading to an appropriate biopsy. Of course it should be remembered that nail matrix melanoma can present as an amelanotic tumour, and therefore any unexplained dystrophy of a single nail should lead to consideration of malignancy.
An inadequate biopsy can impair the pathologist's ability to provide an accurate diagnosis [7] and for this reason the quality of biopsy material is important. Nail plate tissue is routinely placed in a softening agent. If an inexperienced laboratory assistant placed nail matrix in softener, even a carefully collected specimen could be compromised.
As with other melanomas, there is overlap between normal findings and criteria for a diagnosis of melanoma. Both architectural criteria (including with nail matrix melano-