Subungual Pigmented Lesions Require Urgent Specialist Evaluation
Yes, a mole underneath a toenail is concerning and requires urgent referral to a dermatologist or surgeon with expertise in pigmented lesions for evaluation and potential biopsy to rule out subungual melanoma. 1
Why This Is Concerning
Subungual melanomas are particularly dangerous because:
- They are frequently diagnosed late, often at advanced stages, which significantly worsens prognosis 2
- Delays in diagnosis are common because these lesions are often mistakenly treated as other conditions (fungal infections, hematomas) before correct diagnosis 2
- Subungual melanomas have worse outcomes than cutaneous melanomas, with 5-year survival of only 80% versus 100% for cutaneous lesions, largely because they present at greater depths (average 3.68 mm versus 1.36 mm) 2
- Even children can develop subungual melanoma in situ, though rare 3, 4
Red Flags That Demand Immediate Action
You should be particularly concerned if the pigmented lesion shows:
- Rapid growth or darkening of a pigmented nail streak, especially if it results in diffuse melanosis of the nail 3, 5
- Width greater than 3 mm (lesions measuring 9-11 mm are highly suspicious) 5
- Variegated colors ranging from light brown to dark brown to black in a haphazard pattern 3, 5
- Hutchinson's sign (periungual pigmented macule extending onto the skin around the nail) 5
- New onset in adulthood rather than childhood 5
- Presence of ulceration, bleeding, or nodular features 6, 7
What You Should NOT Do
Do not attempt biopsy in primary care. 1, 8
- Punch biopsies and shave biopsies make pathological staging impossible and are explicitly contraindicated 1, 8
- Incisional biopsy has no place in primary care for suspected melanoma 1, 8
- Even superficial sampling can dangerously underestimate Breslow thickness 6
The Correct Approach
Urgent referral without biopsy is the appropriate action:
- Refer immediately to a dermatologist or surgeon with expertise in pigmented lesions 1, 8
- Ensure the patient is seen within 2 weeks of referral 1
- Document the site, size, and clinical features, and photograph the lesion if possible 6, 7
What the Specialist Will Do
Biopsies of possible subungual melanomas must be performed only by surgeons regularly performing such procedures: 1
- The nail plate must be removed sufficiently to expose the underlying lesion 6, 7
- The nail matrix must be adequately sampled, as melanoma arises in this location 6, 7
- Excisional biopsy encompassing the entire lesion is preferred when feasible 6, 7
- For larger lesions, incisional biopsy is acceptable but must include adequate nail matrix sampling 6, 7
Critical Pitfall to Avoid
The most dangerous mistake is dismissing pigmented nail lesions as benign without proper evaluation. While most pigmented nail streaks are benign and remain unchanged, rapidly growing lesions with the features described above can represent early-stage subungual melanoma in situ 3, 5. Early detection through proper biopsy by skilled practitioners can allow complete cure with conservative excision and digit preservation 5, whereas delayed diagnosis leads to advanced disease requiring amputation and carries significantly worse survival 2.