How should a brown wound on the sole of the foot be evaluated and managed?

Evaluation and Management of a Brown Wound on the Sole of the Foot

A brown wound on the sole of the foot requires immediate assessment for malignancy (melanoma), followed by evaluation for infection, ischemia, and underlying osteomyelitis if the lesion is determined to be an ulcer rather than a neoplasm.

Initial Critical Assessment: Rule Out Melanoma

The brown coloration is the most concerning feature and mandates urgent dermatologic evaluation to exclude acral lentiginous melanoma, which commonly presents as a dark pigmented lesion on the plantar surface. This is a clinical priority that supersedes routine wound management, as delayed diagnosis of melanoma dramatically worsens mortality outcomes.

If Confirmed as an Ulcer: Systematic Evaluation

Patient-Level Assessment

• Determine diabetes status immediately, as this fundamentally changes the diagnostic and therapeutic approach 1, 2
• Assess for systemic signs of infection: fever, chills, hypotension, altered mental status, or hyperglycemia (in diabetics) 1
• Document cardiovascular risk factors: smoking, glycemic control (HbA1c if diabetic), prior ulceration or amputation history 2

Limb-Level Vascular Assessment

• Palpate dorsalis pedis and posterior tibial pulses bilaterally 2
• Measure ankle-brachial index (ABI) using Doppler ultrasound; normal is 0.9-1.3 with triphasic waveform 2
• If ABI is unreliable (>1.3 or calcified vessels), measure toe-brachial index (TBI); TBI ≥0.75 excludes significant peripheral arterial disease 2
• Toe systolic pressure <30 mmHg indicates critical ischemia requiring immediate vascular surgery referral, as the wound cannot heal without revascularization 2

Wound-Level Assessment

Diagnose infection based on the presence of purulent secretions OR at least 2 signs of inflammation: erythema, warmth, swelling/induration, tenderness, or pain 1, 3. The brown discoloration itself may represent necrotic tissue, eschar, or hemosiderin staining.

• Probe the wound with a sterile blunt instrument to assess depth and determine if bone is palpable (positive probe-to-bone test suggests osteomyelitis) 2
• Measure and document wound dimensions, depth, presence of undermining or sinus tracts, and surrounding cellulitis extent 1
• Classify infection severity using IDSA/IWGDF criteria: Grade 1 (uninfected), Grade 2 (mild: local infection <2 cm cellulitis), Grade 3 (moderate: >2 cm cellulitis OR deep tissue involvement), Grade 4 (severe: systemic toxicity) 2, 3

Neurological Assessment (if diabetic)

• Test for loss of protective sensation using 10-g monofilament at multiple plantar sites 2
• Perform at least one additional test: pinprick, temperature perception, ankle reflexes, or 128-Hz tuning fork vibratory testing 2

Diagnostic Workup

Imaging

• Obtain plain radiographs of the foot to screen for osteomyelitis, gas in soft tissues, or foreign bodies 1, 2
• MRI is the most sensitive and specific test for osteomyelitis and should be obtained if the probe-to-bone test is positive, the wound is longstanding or deep, or plain films are equivocal 1, 2

Microbiological Sampling (if infected)

• Cleanse and sharply debride the wound before obtaining specimens 1
• Obtain tissue specimens from the debrided wound base via curettage or biopsy—this is superior to swab cultures 1
• Avoid swabbing undebrided ulcers, as this yields unreliable polymicrobial results 1
• Obtain blood cultures if the infection is severe or the patient is systemically ill 1

Immediate Management

Debridement

Sharp surgical debridement is the cornerstone of management and must be performed immediately to remove all necrotic tissue, slough, eschar, and nonviable material 1, 4. The brown discoloration likely represents devitalized tissue requiring excision.

• Repeat debridement at every follow-up visit if nonviable tissue continues to form 1, 4
• Debridement frequency is determined by clinical need, not a fixed schedule 4

Infection Management

• If Grade 3 (moderate) or Grade 4 (severe) infection is present, initiate empiric broad-spectrum intravenous antibiotics immediately targeting gram-positive cocci (especially Staphylococcus aureus), gram-negative bacilli, and anaerobes 1, 5
• Surgical consultation is mandatory for deep tissue abscess, gas, or necrotizing fasciitis 1, 3
• Surgical drainage is definitive treatment for abscess—antibiotics alone will not resolve undrained purulent collections 3

Pressure Offloading

Complete pressure relief from the plantar wound is essential for healing 1. Options include total contact casting, removable cast walkers, or felted foam dressings, depending on infection severity and patient compliance.

Wound Dressing

• Use simple non-adherent dressings (paraffin gauze) or basic absorbent gauze—these perform equally well as expensive specialized dressings 4
• For high-exudate wounds, use foam or alginate dressings for superior absorption 4
• Maintain a moist wound bed while controlling drainage and avoiding tissue maceration 1
• Change dressings frequently enough to achieve these goals 1

Vascular Intervention

If toe pressure is <30 mmHg or TBI is <0.75, refer immediately to vascular surgery for revascularization consideration, as the wound cannot heal with inadequate perfusion 1, 2

Critical Pitfalls to Avoid

• Never assume the brown discoloration is benign—melanoma must be excluded first
• Never delay surgical consultation when infection worsens despite 2-7 days of appropriate antibiotics 3
• Increasing pain is never normal during treatment and mandates immediate reassessment for deep abscess, compartment syndrome, or necrotizing infection 3
• Never rely on antibiotics alone if an abscess is present—surgical drainage is mandatory 3
• Never attempt to heal a plantar wound without adequate pressure offloading—it will fail 1

Follow-Up and Reassessment

If the wound fails to improve after 1-2 weeks of appropriate care, systematically re-evaluate:

• Adequacy of debridement 4
• Presence of unidentified abscess or deeper infection 4
• Unrecognized osteomyelitis 4
• Adequacy of vascular perfusion 1
• Patient compliance with pressure offloading 4

Multidisciplinary team management involving podiatry, vascular surgery, infectious disease, and wound care specialists improves outcomes and reduces amputation rates 1.