Diabetic Foot Infections

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:

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.

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.

⭐ 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.