Acral Lentiginous Melanoma
A non-tender, bruise-like plantar lesion without scaling or texture change should raise immediate concern for acral lentiginous melanoma (ALM) and requires urgent excisional biopsy with a 2mm margin for definitive diagnosis.
Clinical Reasoning
The presentation described—a bruise-like appearance on the plantar surface without scaling or skin texture changes—is a classic red flag for acral lentiginous melanoma, which is notoriously difficult to diagnose early and carries significant mortality risk when delayed.
Why This Matters for Mortality
Acral melanomas are among the most dangerous melanoma subtypes because:
- They are frequently misdiagnosed as benign lesions (bruises, warts, or calluses)
- Delayed diagnosis leads to deeper Breslow thickness at presentation
- Plantar location allows vertical growth before detection
- The absence of typical melanoma features (scaling, texture change) does not exclude malignancy
Diagnostic Approach Using ABCDE Criteria
The guideline-recommended ABCDE criteria apply here 1:
- Asymmetry: Assess if the lesion has irregular shape
- Borders: Look for irregular, poorly defined edges
- Color: Check for heterogeneous pigmentation (brown, black, blue, or violaceous hues)
- Diameter: Note if >7mm (though many early melanomas are smaller 2)
- Evolution: Critical—any recent change in size, color, or shape strongly suggests malignancy 1
The "bruise-like" appearance with heterogeneous color is particularly concerning and fulfills criteria C and potentially E.
Immediate Management
Excisional biopsy is mandatory—never perform a punch or shave biopsy 1. The rationale is clear from guidelines:
- Partial sampling risks missing the thickest portion (Breslow depth determines prognosis)
- Complete histologic assessment is required for accurate staging
- Incisional biopsies can lead to misdiagnosis and compromise treatment planning 1
Technique 1:
- Excise with 2mm normal skin margin
- Use elliptical incision parallel to skin tension lines
- Orient the long axis to facilitate potential re-excision
- Send entire specimen to pathology (never use frozen sections)
- Document excision margins in operative note
Critical Pitfalls to Avoid
- Do not assume it's a bruise or hematoma simply because it lacks tenderness—melanomas are typically painless
- Do not wait for symptoms to develop—by the time bleeding or pain occurs, the lesion is often advanced
- Do not use dermoscopy alone for diagnosis unless you have extensive training; it cannot replace histopathology 1
- Do not perform destructive procedures (laser, electrocautery, cryotherapy) as these prevent accurate histologic assessment 1
Differential Considerations
While the evidence mentions other plantar lesions:
- Plantar vein thrombosis 3: typically tender with subcutaneous nodule (your case is non-tender)
- Primary cutaneous nodular amyloidosis 4: extremely rare, violaceous patches (but typically waxy/firm)
- Plantar lichen planus 5: would show scaling or hyperkeratosis
None of these fit as well as melanoma given the bruise-like appearance without scaling or texture change.
What Happens After Biopsy
If melanoma is confirmed, the histopathology report must include 1:
- Breslow thickness (maximum depth in millimeters)—the single most important prognostic factor
- Ulceration presence
- Clark level of invasion
- Margin clearance status
- Presence of regression
These parameters determine:
- Need for wider re-excision (1cm margin if ≤2mm thick; 2cm if >2mm) 2, 6
- Consideration for sentinel lymph node biopsy if >1mm thickness 2, 6
- Staging workup requirements
Bottom Line
Any pigmented plantar lesion that looks like a bruise but doesn't behave like one (no trauma history, not resolving, or has been present >2-3 weeks) must be biopsied. The stakes are too high—early-stage melanoma is curable with simple excision, but delayed diagnosis dramatically increases mortality risk. When in doubt, excise it out.