1 Introduction

Subungual melanoma is a cutaneous melanoma occurring in the nail bed. It is a rare condition accounting for 1–3% of all melanomas.¹ A meta-analysis of mortality rates for melanoma of the nail unit reported a five-year survival of 77 %.² This poor prognosis is usually attributed to the delay in diagnosis. It most commonly affects the big toe, thumb and index finger.

Traditionally, treatment of choice of subungual melanomas of the fingers have been that of amputation at the proximal joint (metacarpophalangeal or interphalangeal joints). However, this results in poor functional outcomes. Amputation at the interphalangeal joint of the thumb results in a 10 % loss of function in the affected hand, while amputation at the metacarpophalangeal joint results in a 40 % loss of function.³

Recent studies have shown a more conservative approach of a wide local excision, which proves to be successful with low risk of recurrence yet achieving greater functional and aesthetic outcomes,⁴ in the cases of in-situ and minimally invasive subungual melanomas. There are no absolute guidelines existing to guide the management of subungual melanomas yet, although many surgeons perform conservative surgery to maximize the length of the affected digits.

2 Case report

This case report studies such a case of the left little finger nailbed in a Chinese 6-year-old, currently 3 years post-operation following wide excision and reconstruction with full-thickness skin grafting (FTSG).

3 Clinical findings

He initially presented with a single longitudinal melanonychia at birth. There was no history of trauma to the nail prior to presentation. The lesion was treated with watchful waiting initially. It however progressively grew to involve the entire nail bed and hyponychium with a positive Hutchinson sign at the age of 6 years (Fig. 1).

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Fig. 1 Clinical photograph showing left little finger subungual melanoma in-situ in a 6 year old.

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4 Diagnostic assessment

Given the suspicious features, a nail matrix biopsy was done under general anaesthesia. The biopsy was done with a tangential incision made at the proximal nail fold. The nail fold was then reflected to visualise the nail matrix, and a punch biopsy was made encompassing nail plate and underlying matrix down to periosteum. Histopathology results showed melanoma in-situ. Within the nail matrix epithelium, there was confluent proliferation of melanocytes that exhibit significant atypia with enlarged, hyperchromatic nuclei with irregular nuclear contours. Mitoses and dermal invasion were not seen. S100, HMB45 and Melan-A immunohistochemistry highlighted the confluent melanocytic proliferation at the basal to mid epidermis of the nail matrix.

5 Therapeutic intervention

A wide resection was performed under general anaesthesia with the child supine and left arm held out perpendicular to the trunk on a hand table (Fig. 2). A glove tourniquet was placed around the left little finger. A 3-mm skin margin around the lesion was planned. Sharp dissection straight down to bone was performed removing the entire nail apparatus together with the periosteum enbloc using a No. 15 scalpel. There was strictly no undermining of skin or blunt dissection as this would cause contamination, precluding proper local clearance.

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Fig. 2 Clinical photograph showing wide resection of the left little finger subungual melanoma in-situ with preservation of the pulp, tendon insertions and bone.

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Histopathology showed clear margins: proximal 6mm, distal 3mm, ulnar 4mm, radial 3mm, depth 1mm. Extensor and flexor tendon insertions were preserved. The lesion was centered in the nail matrix, comprised of melanocytes with focal pleomorphism and confluent growth, with pagetoid spread up towards the nail plate. No invasion into the dermis was seen. Adjacent to the lesion, there was a benign compound nevus, which showed no significant atypia, and maturation with depth. The lesional cells were strongly and diffusely immunoreactive to HMB-45, Melan A, and S100 immunohistochemical stains. Ki67 immunostain appeared to be focally increased within the lesion.

A full thickness skin graft was taken from the volar wrist horizontally along the skin crease. The size of the surface defect is estimated using sterile tracing paper. The paper is gently pressed against the defect which leaves a blood-stained marked out area. The periphery of the area is then traced out with a sterile skin marker. An alcohol wipe is then dabbed onto the sterile tracing paper. This is then placed against the donor site leaving a mark. We prefer to incorporate this into an elliptical incision to avoid ‘dog-ears’. The skin graft is raised with a No. 15 scalpel without the fat. This minimises the metabolism of the graft and maximises the chances of a good take. This was then secured to the dorsal aspect of the finger using simple interrupted monocryl 5-0. One limb of the suture end was left long and tied over to the opposite stitch to hold down Proflavine-soaked cotton-balls. A bulky dressing with gauze and 2-inch crepe bandage was then applied.

6 Follow-up and outcomes

Post-operatively, the patient was reviewed at 2 weeks. The graft had taken fully and hence was left exposed. We then reviewed the patient at one month and then at three monthly intervals for the first year and then annually. As of the most recent follow up 3 years post-operatively there has been no recurrence (Fig. 3) with absence of axillary and epitrochlear lymphadenopathy. The child has full range of motion and function of the digit.

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Fig. 3 Clinical photograph showing the left little finger at 3 years post-operation including the volar wrist donor site.

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7 Discussion

Paediatric subungual melanomas are extremely rare with only 21 case reports in the literature. While the decision when to biopsy these lesions in children remains controversial, most authors recommend a ‘watchful waiting’ strategy to avoid an unnecessary procedure or risk causing nail dystrophy. Important deciding factors include rapid size progression, pigmentation change, and a positive Hutchinson sign as was seen in our case.^5,6

Multiple studies have shown effective management of subungual melanomas with wide local excision rather than amputation.⁵ In our patient, the use of wide local excision and reconstruction with FTSG appears to be an effective treatment option, achieving good functional and aesthetic outcomes with no signs of recurrence at 3 years post-operatively. Histological clearance is the rule to minimise the risk of recurrence which inadvertently later becomes invasive.^7,8 Surgical margin adequacy has largely been variable. Some quoted being from as little as 5mm and some as thick as 12mm.^8–10 In their paper, Kunishige et al. recommended 9mm margins for trunk and extremity melanoma in-situ.¹⁰ This was because of the worry of subclinical extension which is only detected on histology and as such some surgeons have advocated for Mohs micrographic surgery for all their cases.^8–10 Unfortunately this cannot be applied especially to acral locations and furthermore in the paediatric setting where anatomical size is a factor. In our case, a margin of 9mm in the little finger of a 6-year-old would mean resection of the entire finger pulp compromising preservation of the fingertip. As our case was a known melanoma in-situ and in view of the patient's size, we chose to take margins of 3mm with sharp dissection straight down to bone ensuring no undermining and that the resection was enbloc. The principle was that due to limited anatomy, should margins be inadequate it would have meant an amputation from the outset. Hence for such cases we believe that an attempt at wide resection and reconstruction should be the decision made for the initial surgery. Other surgeons have concurred with this especially for subungual melanoma in-situ in the paediatric age group.^6–8

A FTSG achieves better closure of the wound with greater functional recovery and better aesthetic outcomes of the skin, as compared to a split thickness skin graft (STSG). It has excellent outcomes for coverage of finger defects with bone or tendon exposure.¹¹ Anecdotally for hand and finger defects post lesion resection, we prefer to harvest FTSG from the volar wrist. This is for accessibility and convenience of dressing as it is adjacent to the recipient site. For patients and parents who prefer not to have a horizontal volar wrist scar due to social stigmata, we harvest our FTSG from the cubital fossa. Thus far, the scars from these locations have been cosmetically and functionally acceptable. We have stopped using the medial forearm as a donor site as patients tend to rest their forearms along this area and we find that the scar tends to be sensitive. We also do not use the groin as a donor site as the graft is more pigmented and can develop hair.

8 Conclusion

We recommend considering wide resection and reconstruction with full-thickness skin graft as a viable treatment for pediatric subungual melanoma in-situ.

Financial support and sponsorship

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. The authors have no relevant financial or non-financial interests to disclose.

Informed consent

The study was performed in line with the principles of the Declaration of Helsinki. Approval by our Institutional Ethics Review Board is not necessary as this is a single case. As all data had been anonymised. Consent to participate and to publish were taken and documented in the case notes.

CRediT authorship contribution statement

Yong Ting Pang: Conceptualization, Methodology, Validation, Investigation, Writing – original draft, Writing – review & editing, Visualization, Project administration. Bryan Yeo: Conceptualization, Methodology, Writing – review & editing, Visualization. Neeraj Mishra: Conceptualization, Methodology, Writing – review & editing, Visualization. Mohammad Ashik bin Zainuddin: Conceptualization, Methodology, Writing – review & editing, Visualization. Arjandas Mahadev: Conceptualization, Methodology, Writing – review & editing, Visualization. Kenneth Pak Leung Wong: Conceptualization, Methodology, Validation, Investigation, Writing – original draft, Writing – review & editing, Visualization, Project administration.