Diabetic foot infection

Background

  • 75% of patients have polymicrobial infection, usu 70% are gram positive
  • Ulcer depth is important predictor of healing rate, osteomyelitis (OM) & risk of amputation.
  • Failure of ulcer to heal by 50% or more after 1 month of treatment is a strong predictor that the ulcer is unlikely to heal after 3 months.
  • Recurrence or amputation is 50-70% over 3-5 yrs. Overall, 50-80% will heal within 6 months with optimal care.

Clinical Features

Infection in ulcer bed with mild surrounding erythema (not probe-able to bone)
Classic diabetic plantar ulcer overlying the third metatarsal head with purulent drainage. Ability to probe to bone confirmed osteomyelitis.
Neuropathic diabetic foot ulcer.
  • Diabetes mellitus ulcers usually occur at areas of increased pressure (sole of foot) or friction
    • Venous ulcers usually present above malleoli with irregular borders
    • Arterial ulcers usually found on the toes or shins, with pale, "punched-out" borders (typically painful)
  • Often history of minor/unnoticed trauma such as ill-fitting footwear
  • Note hair and nail growth, determine vascular status (palpate DP, PT, and popliteal pulse)
  • Probe ulceration site, note involvement of bone, joint, tendon, or sinus tract formation
    • Often more extensive than initially appear
    • Use sterile probe, if hit bone chance of OM 90% higher
  • +/- systemic symptoms (e.g. fever, malaise)
  • 50% or more of patients with SEVERE diabetic foot infections will have no systemic signs and symptoms of infection (i.e. fever, tachycardia, leukocytosis, left shift)
  • Diabetes mellitus foot ulcer infection presumed if:
    • 2 or more of following: erythema, warmth, tenderness, or swelling
    • OR if pus coming from ulcer site or nearby sinus tract
  • Severe diabetes mellitus foot infection if:
    • Abnormal vital signs
    • Rim of erythema surrounding ulcer or ulcer >2 cm in diameter
    • Lymphangitic streaking or signs of fasciitis (crepitus, skip lesions, severe tenderness, bullae), or if probe reaches bone/joint/tendon

Differential Diagnosis

Foot infection

Skin and Soft Tissue

Deep Tissue / Limb-Threatening

Bone and Joint

Look A-Likes

Hyperglycemia

Diabetic Emergencies

Diabetes Mellitus (New or Known)

Medication/Drug-Induced

Physiologic Stress Response

  • Sepsis / critical illness (stress hyperglycemia — very common in the ED)
  • Trauma / major surgery / burns
  • Acute coronary syndrome / myocardial infarction
  • Stroke (especially hemorrhagic)
  • Pancreatitis (both a cause and consequence)
  • Shock (any etiology)
  • Pain (catecholamine surge)
  • Seizure (postictal)
  • Physiologic stress alone rarely causes glucose >200 mg/dL in non-diabetics; glucose >200 in a "stress response" should prompt evaluation for undiagnosed diabetes or prediabetes

Endocrine

Pancreatic

  • Pancreatitis (acute or chronic — destruction of islet cells)
  • Pancreatic malignancy (adenocarcinoma, neuroendocrine tumors)
  • Post-pancreatectomy
  • Cystic fibrosis-related diabetes
  • Hemochromatosis (iron deposition in pancreas — "bronze diabetes")

Toxic/Overdose

Other

  • Renal failure (chronic kidney disease, acute kidney injury — impaired insulin clearance AND insulin resistance)
  • Cirrhosis / hepatic failure (impaired glycogenolysis regulation)
  • Pregnancy (gestational diabetes, steroid administration for fetal lung maturity)
  • Parenteral nutrition (TPN, dextrose-containing fluids)
  • Post-transplant diabetes (immunosuppressants)

Complications of Diabetes (Not Causes of Hyperglycemia)

These are associated conditions that may be present alongside hyperglycemia but do not themselves cause elevated glucose:

Evaluation

Workup

  • Obtain ABI on all patients with: nonpalpable DP/PT, claudication symptoms, ischemic foot pain
    • Consider vascular consult if abnormal:
      • ABI <0.4 (severe obstruction)
      • ABI 0.4-0.69 (mod obstruction)

Labs

  • Chem 10, CBC, Coags, A1c, consider ESR/CRP (useful for monitoring response to treatment)
  • ESR >40 increased chance of OM 12 fold, an ESR >70 makes diagnosis nearly certain.

Imaging

  • X-rays to detect soft tissue gas, foreign body, OM, or structural foot deformities
    • OM: x-ray changes occur late in disease, negative xrays do not exclude
  • MRI to eval for OM (not usually done in ED)

Diagnosis

  • Determine presence/extent of infection and likelihood of OM/fasciitis
  • Consider Charcot arthropathy (diabetic neuropathic osteoarthropathy)
    • commonly missed diagnosis
    • requires different management (total contact cast, NWB)

Likelihood of Osteomyelitis

  • Factors that increase likelihood of osteomyelitis:
    • Visible bone or probe to bone
    • Ulcer >2cm in size
    • ESR >70
    • Ulcer duration >2 weeks

Management

Non-infected chronic wounds[1]

  • Prophylactic antibiotics not indicated
  • For clinically uninfected wounds, do not collect a specimen for culture
  • Moist dressing to allow for healing and proper footwear to prevent worsening abrasions

Infected Wounds[1]

  • Consider wound culture prior to starting empiric antibiotic therapy. However cultures may be unnecessary for a mild infection in a patients who have not recently received antibiotic therapy.
  • Coverage is targeted at MSSA + Strep)
  • Strict non-weight bearing, tight glycemic control, meticulous wound care

Severe infection[1]

  • Admit with surgical consult
  • Empiric therapy directed at Pseudomonas aeruginosa is NOT necessary except for patients with risk factors for true infection with this organism
  • MRSA coverage in a patient with a prior history of MRSA infection

Antibiotics

Associated organisms include Staphylococcus, Streptococcus, Enterococcus, Enterobacteriaceae, Proteus, Bacteroides, and Pseudomonas, and Klebsiella

Superficial Mild Infections

Prior antibiotic treatment or moderate infections

Inpatient Treatment

Disposition

  • Non-infected chronic wounds: outpatient management
  • Infected Wounds: Low threshold for admission vs. outpatient management with antibiotics
  • Severe infection: Admit with surgical consult

See Also

External Links

References

  1. ↑ 1.0 1.1 1.2 2012 Infectious Diseases Society of America Clinical Practice Guideline for the Diagnosis and Treatment of Diabetic Foot Infections full text
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