Harvey's Garden

Diabetic foot

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4 min read

Epidemiology & Risk Factors

  • Pathophysiology: Triad of peripheral neuropathy + PAD (ischemia) + trauma/infection.
  • Risk Factors:
    • Poor glycemic control (elevated HbA1c).
    • Loss of Protective Sensation (LOPS) from distal symmetric sensorimotor polyneuropathy.
    • Foot deformities (hammer toes, hallux valgus, Charcot arthropathy).
    • Peripheral artery disease (PAD) & microvascular disease.
    • History of prior DFU or LEA (Lower Extremity Amputation).
  • Microbiology:
    • Mild/Early: Monomicrobial (S. aureus, Streptococcus spp.).
    • Deep/Chronic/Severe: Polymicrobial (Gram-positives + Gram-negatives [Pseudomonas, Enterobacteriaceae] + Anaerobes [Bacteroides]).

Clinical Features

  • Neuropathic Ulcers:
    • Located on plantar pressure points (metatarsal heads, heel).
    • Painless, punched-out base, surrounded by thick hyperkeratotic callus.
  • Ischemic Ulcers:
    • Located on distal tips of toes or lateral foot.
    • Painful (unless masked by neuropathy), necrotic/pale base, decreased/absent pulses, cool extremity, loss of hair.
  • Diabetic Foot Infection (DFI):
    • Local: Warmth, erythema, induration, purulent drainage, foul odor.
    • Systemic: Fever, chills, tachycardia, altered mental status, leukocytosis (may be blunted in DM).
  • Charcot Neuroarthropathy (Neuropathic Arthropathy): c
    • Acute: Warm, swollen, erythematous joint; often misdiagnosed as cellulitis/gout.
    • Chronic: Joint collapse, loss of arch -> pathognomonic “rocker-bottom” foot deformity.
  • Bedside Physical Exam Maneuvers:
    • Semmes-Weinstein 10-g monofilament test: Evaluates for LOPS (screening).
    • Probe-to-bone (PTB) test: Palpating hard, gritty bone with a sterile metal probe; high PPV for contiguous osteomyelitis (OM).

Diagnosis

  • Initial / Bedside Assessment:
    • Probe-to-bone test: If positive in high-risk pt -> clinically diagnostic for OM (warrants imaging & Abx).
    • Vascular Exam: Palpate dorsalis pedis and posterior tibial pulses.
      • Ankle-Brachial Index (ABI): Initial vascular screen. Note: ABI > 1.3 indicates non-compressible/calcified vessels (Mönckeberg sclerosis); must order Toe-Brachial Index (TBI) or arterial duplex.
  • Key Labs:
    • CBC, ESR, CRP (ESR > 70 mm/hr strongly correlates with OM).
    • BMP (assess renal function for imaging contrast & Abx dosing).
    • Wound Cultures: Obtain from deep tissue curettage or bone biopsy after debridement. Superficial swabs are contraindicated (represent colonizers).
  • Imaging:
    • Initial: Plain Radiographs (Foot XR):
      • Evaluates for soft-tissue gas, radio-opaque foreign bodies, Charcot changes, and cortical erosion/periosteal reaction (takes 10-14 days to show OM changes).
      • Typically include osseous fragmentation, new bone formation, and subluxation/dislocation predominantly in the mid and hind foot.
    • Best / Most Sensitive Non-Invasive: MRI of the foot:
      • Test of choice for OM, deep abscess, or joint space infection if XR is negative/indeterminate.
  • Confirmatory / Gold Standard:
    • Bone biopsy and histopathology/culture (via percutaneous or intraoperative approach).

Differential Diagnostics

  • Charcot Neuroarthropathy vs. Cellulitis/OM:
    • Charcot: Warmth/erythema improves with leg elevation for 5-10 minutes; joint effusion and bony destruction on XR without an open ulcer initially.
    • Infection: Erythema persists with elevation; elevated ESR/CRP; open ulcer frequently present.
  • Venous Stasis Ulcer:
    • Located near the medial malleolus; shallow, irregular borders, wet/exudative base, accompanied by stasis dermatitis, hemosiderin deposition, and pedal edema.
  • Arterial (Ischemic) Ulcer:
    • Severe rest pain relieved by dependency; pale base, punched-out borders; absent peripheral pulses.
  • Necrotizing Fasciitis:
    • Pain out of proportion to exam (early), systemic toxicity, skin bullae, crepitus, soft-tissue air on imaging; requires emergent surgical exploration.

Management

  • 1. Acute Infection Management:
    • Mild Infection (Superficial, < 2 cm erythema, no systemic signs):
      • Outpatient oral Abx targeting Staph/Strep: Cephalexin, Amoxicillin-Clavulanate, or Clindamycin.
      • Add TMP-SMX or Doxycycline if MRSA suspected.
    • Moderate to Severe / Deep Infection (Abscess, bone involvement, or systemic signs):
      • Hospital admission, immediate non-weight-bearing.
      • Empiric IV Broad-Spectrum Abx:
        • Vancomycin or Daptomycin (covers MRSA)
        • PLUS Piperacillin-Tazobactam, Cefepime + Metronidazole, or Meropenem (covers Pseudomonas, enteric Gram-negatives, anaerobes).
      • Surgical Intervention (Urgent I&D / Debridement): For deep abscesses, necrotizing infections, compartment syndrome, or non-viable tissue.
  • 2. Chronic Ulcer & Wound Care:
    • Offloading (Cornerstone of healing): Total contact casting (TCC) or specialized non-removable boot.
    • Surgical Debridement: Sharp debridement of devitalized tissue and peripheral hyperkeratosis to promote granulation.
    • Moist Wound Dressings: Hydrogels, alginates, negative-pressure wound therapy (wound VAC).
  • 3. Vascular & Metabolic Optimization:
    • Revascularization: Endovascular angioplasty or surgical bypass if PAD (TcPO2 < 30 mmHg, ABI < 0.4, or non-healing ulcer despite offloading).
    • Glycemic Control: Optimize HbA1c (reduces microvascular complications and aids wound healing).
    • Smoking cessation and lipid management.
  • 4. Refractory / Advanced Disease:
    • Long-term Abx for OM: 4-6 weeks of targeted IV/oral therapy based on bone cultures if bone is not resected.
    • Amputation: Indicated for refractory osteomyelitis, non-reconstructable critical limb ischemia, extensive gangrene, or life-threatening sepsis.

Complications

  • Osteomyelitis, suspected when
    • Positive Probe-to-Bone (PTB) test
    • Ulcer size > 2 cm² or depth > 3 mm.
    • Chronic, non-healing ulcer lasting > 1–2 weeks despite appropriate wound care and offloading. c
    • Visible or exposed bone at the ulcer base.
    • “Sausage toe”: Erythematous, diffusely swollen digit extending beyond the ulcer margins.
    • Deep ulcer overlying a prominent bony landmark (e.g., 1st or 5th metatarsal head, calcaneus).
  • Sepsis and Septic Shock.
  • Necrotizing Soft Tissue Infections (NSTI) / Gas gangrene.
  • Lower Extremity Amputation (LEA) (toe, ray, trans-metatarsal, below-knee).
  • Permanent loss of mobility and high 5-year mortality post-amputation (> 50%).

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