Overview
Diabetic Foot
Quick Reference
Critical Alerts
- Diabetic foot infections can be limb-threatening - rapid progression
- Absence of systemic signs doesn't exclude severe infection - neuropathy masks symptoms
- Probe-to-bone test is highly specific for osteomyelitis
- Broad-spectrum antibiotics for moderate-severe infections
- Surgical debridement often required for limb salvage
Key Diagnostics
- Deep wound culture (before antibiotics if possible)
- X-ray foot (baseline, osteomyelitis)
- MRI foot (gold standard for osteomyelitis)
- HbA1c (glycemic control)
- WBC, ESR, CRP (infection markers)
Emergency Treatments
- Wound care: Debridement, offloading
- Antibiotics: Based on severity and culture
- Surgical consultation: For abscess, deep infection, osteomyelitis
- Glycemic control: Insulin sliding scale or drip
- Vascular assessment: May need revascularization
Definition
Diabetic foot refers to a spectrum of pathological conditions affecting the foot in patients with diabetes mellitus, including neuropathy, ischemia, infection, and ulceration. Diabetic foot infection (DFI) is a particularly serious complication that is the most common cause of non-traumatic lower extremity amputation.
Classification Systems
IDSA/IWGDF Infection Severity Classification
| Grade | Severity | Description |
|---|---|---|
| 1 | Uninfected | No purulence or inflammation |
| 2 | Mild | Local infection only; cellulitis <2 cm |
| 3 | Moderate | Cellulitis > cm, deep tissue involvement, no systemic signs |
| 4 | Severe | Any infection with systemic inflammatory response (SIRS) |
Epidemiology
- Diabetes prevalence: 10% of population
- Foot ulcers: 15-25% of diabetics develop during lifetime
- Infection: 50-60% of ulcers become infected
- Amputation: 85% preceded by foot ulcer
- Mortality (post-amputation): 50% at 5 years
Pathophysiology
Triad of Diabetic Foot Disease
1. Neuropathy (Most Common)
- Sensory: Loss of protective sensation
- Motor: Intrinsic muscle atrophy, foot deformities
- Autonomic: Dry skin, altered sweating
2. Peripheral Arterial Disease (PAD)
- Macrovascular disease
- Reduced blood flow
- Impaired wound healing
- Ischemic ulcers
3. Immunopathy
- Impaired leukocyte function
- Reduced chemotaxis
- Impaired phagocytosis
- Increased susceptibility to infection
Pathway to Ulceration and Infection
Neuropathy → Loss of protective sensation
↓
Mechanical stress + Minor trauma (unnoticed)
↓
Ulcer forms
↓
Hyperglycemia + Immunopathy + PAD
↓
Delayed healing + Infection
↓
Deep tissue spread → Osteomyelitis → Gangrene
↓
Amputation risk
Microbiology
Mild Infections (Superficial)
- Gram-positive cocci: S. aureus, Streptococci
- Often monomicrobial
Moderate-Severe or Chronic Infections
- Polymicrobial
- S. aureus (including MRSA)
- Streptococci
- Enterococci
- Gram-negative rods (E. coli, Proteus, Klebsiella)
- Anaerobes (especially if necrotic or deep)
- Pseudomonas (water exposure, chronic)
Clinical Presentation
History
Key Questions
Signs of Infection
| Finding | Significance |
|---|---|
| Purulent discharge | Infection present |
| Erythema (≥0.5 cm around wound) | Cellulitis |
| Warmth | Inflammation/infection |
| Swelling | Infection, may indicate deep involvement |
| Foul odor | Anaerobic infection, necrosis |
| Crepitus | Gas-forming organisms (emergency) |
| Fluctuance | Abscess |
| Exposed bone | Osteomyelitis highly likely |
Ulcer Assessment
| Parameter | Description |
|---|---|
| Location | Plantar (neuropathic), tips of toes (ischemic) |
| Size | Measure in cm |
| Depth | Superficial, tendon, bone |
| Drainage | Serous, purulent, sanguineous |
| Surrounding tissue | Cellulitis extent, maceration |
| Wound bed | Granulation, slough, necrosis |
Probe-to-Bone (PTB) Test
Technique: Insert sterile metal probe into wound
Vascular Assessment
| Finding | Suggests |
|---|---|
| Absent pedal pulses | PAD |
| Cool, hairless extremity | Ischemia |
| Thin, shiny skin | Chronic ischemia |
| Delayed capillary refill | Poor perfusion |
| ABI <0.9 | PAD present |
| ABI >.3 | Calcified vessels (falsely elevated) |
Duration of ulcer
Common presentation.
Previous ulcers/infections
Common presentation.
Prior amputations
Common presentation.
Diabetes duration and control
Common presentation.
Symptoms
pain (may be absent), discharge, odor
Systemic symptoms
fever, chills, malaise
Vascular history
claudication, rest pain
Recent foot care, trauma
Common presentation.
Red Flags (Life-Threatening)
Limb-Threatening Infections
| Red Flag | Concern | Action |
|---|---|---|
| Rapidly spreading cellulitis | Necrotizing fasciitis | Emergent surgery |
| Crepitus | Gas gangrene | Emergent surgery |
| Gas on X-ray | Necrotizing infection | Emergent surgery |
| Deep abscess | Deep space infection | Surgical drainage |
| Exposed bone + purulence | Osteomyelitis | Antibiotics, likely surgery |
| Signs of sepsis | Systemic infection | Sepsis protocol |
| Wet gangrene | Infected necrosis | Emergent amputation may be needed |
Sepsis in Diabetic Foot Infection
- May occur without fever (immunocompromise)
- Tachycardia, hypotension, altered mental status
- Lactate elevation
- IV antibiotics STAT, fluid resuscitation
Differential Diagnosis
Other Causes of Foot Ulcers
| Condition | Features |
|---|---|
| Venous ulcer | Medial malleolus, edema, stasis changes |
| Arterial ulcer | Painful, distal, punched-out |
| Pressure ulcer | Over bony prominences |
| Neuropathic (non-diabetic) | B12 deficiency, alcohol, other causes |
| Traumatic | History of injury |
| Malignancy | Non-healing, atypical |
Infections Mimicking Diabetic Foot
- Cellulitis from other causes
- Gout (acute, painful, swollen joint)
- Charcot foot (acute) - can mimic infection
- Deep vein thrombosis
Charcot Neuroarthropathy
| Feature | Charcot | Infection |
|---|---|---|
| Swelling | Diffuse | May be localized |
| Erythema | Often bilateral | Usually unilateral |
| Temperature | Warm (but often bilateral) | Warm |
| Pain | Often painless | Often painless in diabetics |
| Ulcer | May be absent | Usually present |
| WBC | Normal | Often elevated |
| X-ray | Joint destruction, fragmentation | Osteomyelitis changes |
Diagnostic Approach
Laboratory Studies
| Test | Purpose |
|---|---|
| CBC | WBC may be elevated (not always) |
| BMP | Renal function (affects antibiotic choice) |
| HbA1c | Glycemic control |
| ESR | >0 mm/hr suggests osteomyelitis |
| CRP | Marker of inflammation |
| Procalcitonin | May help distinguish infection severity |
| Blood cultures | If septic or severe infection |
Wound Culture
Best Practice
- Obtain BEFORE starting antibiotics (if possible)
- Curettage or deep tissue sample preferred
- Surface swabs are less reliable (colonization)
- Send for aerobic + anaerobic culture
Imaging
Plain X-ray (First-Line)
| Finding | Significance |
|---|---|
| Soft tissue gas | Emergency - necrotizing infection |
| Foreign body | May need removal |
| Osteomyelitis signs | Cortical erosion, periosteal reaction (late finding) |
| Charcot changes | Joint destruction |
MRI Foot (Gold Standard for Osteomyelitis)
- Sensitivity 90%, Specificity 80-85%
- Marrow edema (T1 low, STIR high)
- Cortical disruption
- Differentiates Charcot from osteomyelitis (sometimes difficult)
Bone Scan
- Sensitive but not specific
- Use if MRI contraindicated
Vascular Studies
| Test | Purpose |
|---|---|
| ABI (ankle-brachial index) | Assess for PAD |
| Toe pressures | More accurate in diabetics (calcified vessels) |
| Doppler ultrasound | Arterial patency |
| CTA/MRA | Surgical planning for revascularization |
Treatment
Wound Care
Local Care
1. Debride necrotic tissue (sharp, surgical, or enzymatic)
2. Cleanse wound
3. Apply appropriate dressings (based on wound characteristics)
4. Offload pressure (total contact cast, removable walker, wheelchair)
5. Keep wound moist (moist wound healing)
Antibiotic Therapy
Mild Infection (Oral, Outpatient)
| Regimen | Coverage |
|---|---|
| Amoxicillin-clavulanate 875/125 mg BID | Gram-positive + anaerobes |
| OR Cephalexin 500 mg QID | Gram-positive |
| OR Doxycycline 100 mg BID | Gram-positive including MRSA |
| OR TMP-SMX DS 1 tab BID | MRSA coverage |
Moderate Infection (IV then Oral)
| Regimen | Coverage |
|---|---|
| Ampicillin-sulbactam 3g IV q6h | Broad (not MRSA) |
| OR Piperacillin-tazobactam 3.375g IV q6h | Broad including Pseudomonas |
| PLUS Vancomycin 15-20 mg/kg IV q12h | Add for MRSA risk |
Severe Infection (IV)
| Regimen | Coverage |
|---|---|
| Vancomycin + Piperacillin-tazobactam | MRSA + broad Gram-negative + anaerobes |
| OR Vancomycin + Meropenem | Resistant organisms |
Duration
| Condition | Duration |
|---|---|
| Soft tissue only | 1-2 weeks |
| Osteomyelitis (surgical resection) | 2-4 weeks post-surgery |
| Osteomyelitis (no surgery) | 6 weeks minimum |
Surgical Consultation
Indications for Surgery
- Deep abscess
- Extensive necrosis
- Crepitus or gas
- Necrotizing fasciitis
- Osteomyelitis requiring debridement
- Failure of medical management
- Amputation if limb not salvageable
Glycemic Control
- Hyperglycemia impairs wound healing and immune function
- Insulin sliding scale or IV insulin drip for severe cases
- Target glucose <180 mg/dL in acute infection
Vascular Intervention
If PAD Present
- Revascularization may be limb-saving
- Endovascular (angioplasty/stent) or surgical bypass
- Consult vascular surgery
Disposition
Admission Criteria
- Moderate to severe infection (IDSA Grade 3-4)
- Sepsis or systemic toxicity
- Need for IV antibiotics
- Need for surgical debridement
- Limb-threatening ischemia
- Unreliable patient or poor social support
- Osteomyelitis requiring workup/treatment
Outpatient Management
- Mild infection (Grade 2)
- Reliable patient with good follow-up
- Able to perform wound care
- No systemic signs
- Close follow-up in 2-3 days
Follow-up Recommendations
| Timeframe | Purpose |
|---|---|
| 2-3 days | Reassess wound, antibiotic response |
| Weekly | Until healed |
| Ongoing | Podiatry, diabetes management |
Patient Education
Understanding Diabetic Foot Disease
- Diabetes can damage nerves and blood vessels in your feet
- You may not feel injuries, so you need to check your feet daily
- Infections can spread quickly and lead to amputation if not treated
- Good blood sugar control helps prevent complications
Daily Foot Care
- Inspect feet daily (use mirror if needed)
- Wash and dry feet thoroughly
- Apply moisturizer (not between toes)
- Never go barefoot
- Wear well-fitting shoes
- Check inside shoes for foreign objects
- Trim nails straight across
When to Seek Care
- Any cut, blister, or sore
- Redness, swelling, warmth
- Discharge or foul odor
- New pain (or pain in usually numb areas)
- Color changes (pale, blue, black)
- Fever
Special Populations
End-Stage Renal Disease
- Higher infection risk
- Antibiotic dosing adjustments
- Often have severe PAD
- Calciphylaxis mimics infection
Immunocompromised
- Broader antibiotic coverage
- Lower threshold for imaging and admission
- Atypical organisms possible
Charcot Foot
- May coexist with infection
- MRI helpful but can be difficult to distinguish
- Offloading essential
- Avoid weight-bearing
Failed Previous Treatment
- Consider resistance
- Re-culture wound
- Reassess for osteomyelitis
- Consider surgical debridement
- Vascular assessment
Quality Metrics
Performance Indicators
| Metric | Target |
|---|---|
| Deep wound culture obtained | >0% moderate-severe |
| X-ray for moderate-severe infection | 100% |
| Antibiotics within 2 hours for severe | 100% |
| Surgical consult for severe/abscess | Same day |
| Glycemic control addressed | 100% |
| Vascular assessment documented | >0% |
Documentation Requirements
- Detailed wound description (size, depth, drainage)
- Surrounding tissue assessment
- Probe-to-bone test result
- Pulses and vascular status
- Infection severity classification
- Antibiotic chosen and rationale
- Surgical consultation if indicated
- Discharge instructions and follow-up
Key Clinical Pearls
Diagnostic Pearls
- Neuropathy masks pain - absence of pain doesn't mean absence of infection
- Probe-to-bone positive = osteomyelitis until proven otherwise
- X-ray changes of osteomyelitis are late - MRI is more sensitive
- Crepitus or gas on imaging = emergent surgery
- Always check pulses - ischemia affects healing
Treatment Pearls
- Broad-spectrum antibiotics for moderate-severe infections
- MRSA coverage if history of MRSA or high local prevalence
- Surgical debridement often necessary for moderate-severe
- Offloading pressure is essential for healing
- Glycemic control improves infection outcomes
Disposition Pearls
- Low threshold for admission - infections progress rapidly
- Mild infections can be outpatient with close follow-up
- Sepsis = ICU with IV antibiotics and possible surgery
- Multidisciplinary care (ID, surgery, vascular, podiatry)
- Prevention education is key to reduce recurrence
References
- Lipsky BA, et al. 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clin Infect Dis. 2012;54(12):e132-173.
- Lipsky BA, et al. IWGDF guidance on the diagnosis and management of foot infections in persons with diabetes. Diabetes Metab Res Rev. 2020;36(S1):e3280.
- Armstrong DG, et al. Diabetic foot ulcers and their recurrence. N Engl J Med. 2017;376(24):2367-2375.
- Lavery LA, et al. Probe-to-bone test for diagnosing diabetic foot osteomyelitis. Diabetes Care. 2007;30(2):270-274.
- Prompers L, et al. High prevalence of ischaemia, infection and serious comorbidity in patients with diabetic foot disease in Europe. Diabetologia. 2007;50(1):18-25.
- Reiber GE, et al. Causal pathways for incident lower-extremity ulcers in patients with diabetes. Diabetes Care. 1999;22(1):157-162.
Version History
| Version | Date | Changes |
|---|---|---|
| 1.0 | 2025-01-15 | Initial comprehensive version with 14-section template |