Diabetic foot infection

Background

  • 1st key factor is to assess extent and depth of ulcer (typically more extensive than they appear)
    • 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 mos.
  • 75% of patients have polymicrobial infection, usu 70% are gram positive
  • 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)
  • Recurrence of amputation is 50-70% over 3-5 yrs. Overall, 50-80% will heal within 6 mos with optimal care.
  • 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)

Clinical Features

HPI

  • Ask about recent trauma
  • Duration of current lesions
  • Associated systemic symptoms
  • Prior treatments

Physical Exam

  • Determine ulcer location, dimensions, depth, and appearance
  • 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
    • Use sterile probe, if hit bone chance of OM 90% higher

Differential Diagnosis

Foot infection

Look A-Likes

Hyperglycemia

Evaluation

  • 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)
  • 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 TTP, bullae), or if probe reaches bone/joint/tendon
  • Obtain ABI on all patients with: nonpalpable DP/PT, claudication symptoms, ischemic foot pain
    • Call vascular if:
      • ABI <0.4 (severe obstruction)
      • ABI 0.4-0.69 (mod obstruction)

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)

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.

Likelihood of OM

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

Management

Noninfected chronic wounds[1]

  • Prophylactic antibiotics not indcated
  • 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

See Also

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