Immediate Biopsy is Required
A non-tender, bruise-like patch on the sole that appeared within the past week without nodules requires urgent excisional biopsy to rule out acral melanoma, which can present as a flat pigmented lesion mimicking benign conditions. 1, 2
Why This Matters: Acral Melanoma is Easily Missed
Acral melanoma (melanoma of palms, soles, and nail beds) is particularly dangerous because:
- It presents as flat, bruise-like patches rather than raised nodules, making it clinically deceptive 3
- It occurs in sun-protected areas and affects all skin types, including darker-skinned individuals 1
- Early detection is critical—survival depends entirely on stage at diagnosis 1
- The sole is a high-risk location where melanoma frequently occurs 4
The 7mm Rule and When to Biopsy Immediately
Based on validated screening criteria for plantar melanocytic lesions 4:
Biopsy immediately if ANY of the following apply:
- Lesion >7mm in maximum diameter
- Marked irregularity in shape or color (even if ≤7mm)
- Recent appearance or change in a pigmented lesion
- Parallel ridge pattern on dermoscopy (highly specific for acral melanoma)
Your case triggers immediate biopsy because it appeared within the past week (recent onset/dynamics) and presents as an atypical bruise-like patch—both red flags per the ABCD criteria (Asymmetry, Border irregularity, Color heterogeneity, Dynamics/evolution) 2.
Critical Pitfall: Don't Wait and Watch
The most dangerous error is assuming this is a benign bruise or hematoma and adopting a "wait and see" approach. Acral melanomas are frequently misdiagnosed initially because 3:
- They mimic traumatic bruises, warts, or other benign conditions
- Patients often attribute them to minor trauma (as in your case)
- The absence of nodules provides false reassurance
The Correct Biopsy Technique
Perform a complete excisional biopsy with narrow margins (not a shave or punch biopsy) 2:
- Full-thickness excision allows proper Breslow depth measurement
- Include a small side margin (2-3mm)
- Send to an experienced dermatopathology laboratory
- Request assessment of: Breslow thickness, ulceration, mitotic rate, margins 2
What Dermoscopy Should Show
If dermoscopy is available before biopsy, look for 4, 3:
- Parallel ridge pattern = highly suspicious for melanoma
- Irregular pigmentation patterns
- Polymorphic vessels
- Absence of typical nevus patterns
However, dermoscopy findings should not delay biopsy—proceed directly to excisional biopsy given the clinical presentation.
Alternative Diagnoses Are Less Likely But Considered
While acral melanoma is the must-not-miss diagnosis, the differential includes:
- Traumatic hematoma (but typically resolves within 2-3 weeks)
- Lichen planus (usually pruritic, multiple lesions) 5
- Patch-type granuloma annulare (extremely rare on sole, typically asymptomatic) 6
None of these alternatives change management: biopsy is still required because clinical examination alone cannot reliably exclude melanoma 2, 4.
Timeline Matters
The one-week timeline is concerning because:
- True traumatic bruises evolve through color changes (red→purple→green→yellow) over 2-3 weeks
- Melanomas can present acutely but don't resolve spontaneously
- If this doesn't show typical bruise evolution within 2 weeks, biopsy becomes even more urgent
Do not delay beyond 1-2 weeks for biopsy, regardless of evolution pattern.