Diabetic Foot Infections

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Pathophysiology - Sugar & Sores

  • Core Triad (Fuelled by Hyperglycemia):
    • Neuropathy: Sensory (↓sensation → unnoticed trauma), motor (deformities → pressure points), autonomic (↓sweat → skin cracks).
    • Angiopathy (PAD): ↓blood flow → impaired healing & antibiotic delivery.
    • Immunodeficiency: Impaired neutrophil function (chemotaxis, phagocytosis), ↓host defense.
  • Result: Minor trauma + poor wound healing + ↓immune response → infection.
  • Chronic hyperglycemia → Advanced Glycation End-products (AGEs) → tissue damage.

⭐ Sensory neuropathy is the most common initiating factor for diabetic foot ulcers.

Microbiology - Tiny Terrors

  • Typically polymicrobial; complexity ↑ with severity/chronicity.
  • Most Common Isolates:
    • Staphylococcus aureus (incl. MRSA).
    • β-hemolytic Streptococci (Groups A, B).
  • In Deeper/Chronic Wounds, Add:
    • Gram-negative bacilli: Pseudomonas aeruginosa, Enterobacteriaceae (E. coli, Klebsiella).
    • Anaerobes: Bacteroides spp., Peptostreptococcus spp.
  • Empirical therapy must cover these; tailor with culture results.

Pseudomonas aeruginosa is frequently isolated from DFI, especially in patients with prior antibiotic use or prolonged hospitalisation.

Clinical & Classification - Signs & Stages

  • Local Signs of Infection:
    • Erythema (>0.5 cm around ulcer), warmth, swelling/induration.
    • Tenderness/pain (neuropathy may mask).
    • Purulent discharge, fluctuance, crepitus (rare, severe).
  • Systemic Signs (Severe Infection): Fever (>38°C), chills, tachycardia (>90 bpm), leukocytosis (>12,000 cells/mm³).
  • Classification Highlights:
SystemKey Infection Indicators
WagnerGrade 0: High-risk foot.
Grade 1: Superficial ulcer.
Grade 2: Ulcer to tendon/capsule.
Grade 3: Deep ulcer with abscess, osteomyelitis.
IDSA/PEDIS (Infection Severity)Mild: ≥2 inflammation signs (e.g., erythema 0.5-2 cm); cellulitis <2 cm.
Moderate: Erythema >2 cm, or deep structure involvement (abscess, osteomyelitis, septic arthritis); no SIRS.
Severe: Any local infection + ≥2 SIRS criteria.

Diagnosis - Sleuthing Sepsis

  • Clinical Exam: Signs of infection (warmth, erythema, swelling, purulence). Ulcer >2 cm² or >3 mm deep?
  • Probe-to-Bone (PTB) Test: Positive if bone palpated; high specificity for osteomyelitis.
  • Imaging:
    • X-ray: Initial; may show gas, foreign bodies, late osteomyelitis signs.
    • MRI: Gold standard for osteomyelitis; details soft tissue/bone extent.
  • Labs: ↑ESR, ↑CRP (non-specific, monitor therapy).
  • Microbiology: Deep tissue/bone biopsy for culture (avoid superficial swabs).

    ⭐ A positive probe-to-bone test has high specificity (~85-90%) for osteomyelitis in DFU. Osteomyelitis vs Active Charcot Foot

Management & Prevention - Healing & Halting

  • Comprehensive Management:
    • Systemic: Aggressive glycemic control (HbA1c <7%); Empiric broad-spectrum IV/oral antibiotics, then culture-guided.
    • Local Wound Care: Surgical/enzymatic debridement of non-viable tissue; Appropriate dressings (moist healing).
    • Pressure Reduction: Total Contact Cast (TCC) gold standard for offloading neuropathic ulcers.
    • Vascular Assessment: ABI, Doppler; Revascularization (angioplasty/bypass) for significant PAD.
    • Surgery: Amputation for extensive necrosis, sepsis, or failed conservative therapy.
  • Crucial Prevention:
    • Daily self-foot examination; Proper nail/skin care; Appropriate, well-fitting footwear.
    • Regular clinical foot checks (monofilament, pulses); Patient education on risk factors.

4 Essentials for Preventing Diabetic Foot Ulcers

⭐ In diabetic foot osteomyelitis, MRI is the most sensitive imaging, but a positive probe-to-bone test (PTB) has high specificity (~85-90%).

High‑Yield Points - ⚡ Biggest Takeaways

  • DFIs are typically polymicrobial; Staphylococcus aureus and Streptococci are common.
  • Peripheral neuropathy (sensory loss) and Peripheral Arterial Disease (PAD) (impaired healing) are major predisposing factors.
  • Suspect osteomyelitis with deep ulcers or positive probe-to-bone test; MRI is the investigation of choice for confirmation.
  • Management pillars: aggressive debridement, empiric broad-spectrum antibiotics, strict glycemic control, and offloading pressure.
  • Charcot neuroarthropathy can mimic infection, presenting as a warm, swollen, erythematous foot without pus.
  • Severity is commonly graded using Wagner or University of Texas (UT) classification systems.
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Practice Questions: Diabetic Foot Infections

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A 60-year-old person who completed treatment for leprosy many years ago now presents with a punched-out, painless ulcer on the sole of his foot. What is the most appropriate management?

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Flashcards: Diabetic Foot Infections

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Osteomyelitis of the _____ is more often seen in adults

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Osteomyelitis of the _____ is more often seen in adults

frontal bone (facial bone)

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