Subungual Melanoma: Clinical Presentation and Recognition
I cannot provide actual images, but I can describe the key clinical features of subungual melanoma (melanoma of the nails) to help you recognize this potentially deadly condition.
Key Clinical Features to Recognize
Subungual melanoma most commonly presents as longitudinal melanonychia (a brown-to-black pigmented band running from the cuticle to the nail tip), though it can also appear as nail dystrophy, ulceration, or amelanotic (non-pigmented) lesions 1, 2.
Classic Warning Signs
Look for these specific features that distinguish malignant from benign nail pigmentation:
- Hutchinson's sign: Pigmentation extending from the nail onto the surrounding periungual skin (cuticle, nail fold, or lateral nail groove) - this is highly suspicious for melanoma 3
- Width >3mm of the pigmented band
- Irregular borders with blurred or variegated edges of the pigmented band
- Color variation within the band (multiple shades of brown, black, or gray)
- Rapid change in size, color, or morphology over weeks to months 4, 5
- Single digit involvement in adults (benign melanonychia is often multiple digits)
- Thumb or great toe location (most common sites) 5, 6
Atypical Presentations That Cause Diagnostic Delay
Be aware that subungual melanoma frequently masquerades as benign conditions:
- Chronic paronychia or "infected nail" with persistent swelling and serous drainage 4, 5
- Onychomycosis (fungal nail infection) with nail dystrophy 5, 7
- Trauma-related changes with nail bed ulceration or granulation tissue 4
- Amelanotic (non-pigmented) presentations appearing as red, friable masses under the nail 7
- Wart-like or hyperkeratotic lesions 8
Critical Diagnostic Approach
When evaluating any suspicious nail lesion, maintain a low threshold for nail matrix biopsy 9, 4. The diagnostic algorithm should be:
- Clinical examination: Document the specific features above, photograph the lesion
- Dermoscopy by experienced physician enhances diagnostic accuracy 1, 2
- Nail matrix biopsy: Remove sufficient nail plate to adequately sample the nail matrix where melanoma arises 9, 10, 11
- Full-thickness excisional biopsy when possible, as partial sampling risks misdiagnosis 12
Common Diagnostic Pitfalls
The most dangerous error is attributing persistent nail changes to benign conditions without biopsy confirmation 4, 5, 7. Key mistakes include:
- Treating presumed "chronic onychia" or "onychomycosis" for months to years without improvement
- Accepting negative PET-CT as ruling out malignancy (early melanoma may not show on imaging) 4
- Performing superficial shave biopsies that miss the diagnosis 9
- Assuming trauma explains all findings without considering post-traumatic melanoma development 4
Any nail lesion that fails to respond to appropriate treatment within 6-8 weeks requires biopsy to exclude malignancy 4, 5.
Special Populations
In pediatric patients, the approach differs significantly: subungual melanoma is extraordinarily rare (only 21 cases reported), and most longitudinal melanonychia in children is benign 13. A watch-and-wait strategy with close monitoring is often appropriate in children, whereas in adults over 50 years, any new or changing longitudinal melanonychia should be biopsied 6, 13.
Acrolentiginous melanoma (the subtype affecting nails) has distinct molecular features with lower rates of BRAF mutations and potential c-Kit mutations, which becomes relevant for advanced disease treatment 1, 2.