Subungual melanoma
Nail unit melanoma; ungual melanoma
Subungual melanoma is a melanoma of the nail apparatus (most commonly the nail matrix). It accounts for ~1–3% of melanomas in white populations but up to 15–25% in skin-of-colour populations. Frequent misdiagnosis as subungual haematoma, fungal nail or paronychia leads to delayed presentation. Most are acral lentiginous histologically. Hutchinson's sign — pigment extension onto the nail fold — is a key clue. Digit-preserving nail-unit excision can be considered for melanoma in situ; invasive disease should be planned through the melanoma MDT, with oncological clearance taking priority over reconstruction.
Clinical features
- Most often the great toe (~half), then thumb (~25%); subungual ALM is not UV-driven — site predilection is generally attributed to cumulative mechanical trauma exposure at these digits, not sun exposure.
- Longitudinal melanonychia — a brown/black band running the length of the nail. Concerning features:
- Width ≥ 3 mm in adults (per the ABCDEF rule for subungual melanoma — Age/race, Brown-black band ≥ 3 mm / Border irregularity, Change, Digit involvement (thumb / index / hallux), Extension of pigment (Hutchinson), Family / personal history)
- Variegated colour, irregular borders
- Triangular shape (wider proximally)
- Rapid change
- Single digit in adult; thumb / great toe
- Hutchinson's sign: extension of pigment onto the proximal or lateral nail fold — strongly suggestive of melanoma.
- Nail dystrophy, plate splitting or bleeding may be late features.
- Amelanotic subungual melanoma (~25%) presents as a non-healing nodule, granulation, ulceration or chronic paronychia — often misdiagnosed.
Differential diagnosis
- Subungual haematoma — usually traumatic, dark red-brown, grows out distally, sharp proximal edge.
- Fungal melanonychia (e.g. Trichophyton rubrum nigricans) — confirm with mycology.
- Drug-induced melanonychia — chemotherapy, antimalarials, AZT.
- Benign racial melanonychia (multiple digits, symmetrical).
- Benign nail matrix naevus (children commonly; usually regular thin band).
- Glomus tumour (red/blue, exquisitely tender to cold and pressure).
Biopsy technique
- Nail-plate avulsion (proximal half) to expose the matrix.
- Lesion-guided biopsy of pigment origin in the matrix:
- Lateral 3 mm punch for narrow lateral bands.
- Tangential matrix shave for wider bands.
- Full longitudinal lateral matrix excision for lateral bands.
- Transverse proximal matrix excision for central bands.
- Mark orientation; submit clearly labelled to a histopathologist familiar with nail specimens.
- Counsel about risk of post-biopsy nail dystrophy.
Surgical management
Traditional
- Distal interphalangeal-joint disarticulation for digits other than thumb.
- For the thumb, IP-joint disarticulation preserves length and grip.
Melanoma in situ
- For melanoma in situ, digit-preserving excision of the nail apparatus with margin control and full-thickness skin graft or local flap reconstruction can be considered in specialist hands.
- The aim is to preserve digital length, dexterity and proprioception where this does not compromise oncological clearance.
- Should be performed by a hand / foot surgeon in conjunction with the skin cancer MDT.
Invasive disease
- Do not assume digit preservation is appropriate for invasive subungual melanoma. Management depends on Breslow thickness, ulceration, anatomical extent, bone / joint involvement, imaging and MDT assessment.
- Amputation remains appropriate where bone, joint or functionally critical deep structures are involved, or where oncologically adequate clearance cannot otherwise be achieved.
Sentinel node
- Discuss SLNB according to NICE NG14: consider for Breslow 0.8–1.0 mm with ulceration, lymphovascular invasion or mitotic index ≥2, and for Breslow >1.0 mm; lymphatic mapping from digits can be more variable than for trunk/limb.
Prognosis
5-year survival ranges 50–80% depending on Breslow thickness — typically worse than non-acral cutaneous melanoma due to delayed presentation. Education of clinicians (and the public) to consider melanoma in any single-digit pigmented or non-healing nail lesion is the most effective intervention.
References
- Levit EK et al. The ABC rule for clinical detection of subungual melanoma. J Am Acad Dermatol; 2000.
- Cochran AM et al. Subungual melanoma: a review of current treatment. Plast Reconstr Surg; 2014.
- Lazar A et al. Functional surgery for in situ subungual melanoma. Ann Surg Oncol; 2017.
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