Diabetic Foot Infection

Background

• Diabetic foot infection refers to any infection in the foot of a patient with diabetes mellitus ranging from superficial wound infection to osteomyelitis.
• Most infections arise in the setting of trauma or in areas of ulceration that have resulted from peripheral neuropathy.
• Peripheral neuropathy and peripheral vascular disease are major risk factors for infection and are present in over half of patients with infected foot wounds.
• Other factors that increase the likelihood of infection in a foot wound include trauma, history of walking barefoot, recurrent ulcers or ulcers that have been present > 30 days, prior lower extremity amputation, and chronic renal insufficiency.

Evaluation

• Suspect the possibility of infection when evaluating any foot wound in a patient with diabetes mellitus (Strong recommendation).
• Assess all wounds for:
  • classic signs of infection including redness, warmth, tenderness, pain, and purulence
  • secondary signs of infection including nonpurulent secretions, friable or discolored granulation tissue, erosive wound edges, and foul odor
• Infected wounds are typically defined as one with ≥ 2 classic signs but the definition is often expanded to include secondary signs, particularly for patients with peripheral neuropathy in whom classic signs may be absent.
• Use a validated classification system, such as the IDSA/IWGDF system, to help determine wound severity and its relation to outcome (Strong recommendation).
• Perform careful assessment of the extent and depth of infection, evaluating specifically for osteomyelitis.
  • Features that should raise suspicion of osteomyelitis include presence of a nonhealing ulcer after 6 weeks of wound care, particularly in those with inadequate blood supply, a large ulcer area, and/or exposed bone.
  • On physical examination, consider a probe-to-bone test using a sterile blunt metal probe. The presence of palpable or visible bone is highly predictive of osteomyelitis.
  • Perform X-ray all patients to look for bony abnormalities suggestive of osteomyelitis, as well as soft tissue gas and foreign bodies (Strong recommendation).
  • Use magnetic resonance imaging (MRI) when the suspicion for osteomyelitis is high and that diagnosis is not clear by physical exam or x-ray, or when there is suspicion for complications such as an abscess.
  • A definitive diagnosis of osteomyelitis requires a bone biopsy (Strong recommendation).
• Evaluate for systemic infection.
  • Signs of systemic infection include fever, chills, hemodynamic instability, and metabolic derangements such as hyperglycemia and electrolyte abnormalities.
  • Blood tests suggesting systemic infection or osteomyelitis include leukocytosis and elevated inflammatory markers (for example, erythrocyte sedimentation rate [ESR], C-reactive protein [CRP]).
• Assess for peripheral artery disease, which is both a risk factor of infection and may require intervention for the ulcer and the infection to heal.
• Palpate femoral, popliteal, and pedal pulses. Perform ankle-brachial index (ABI) using a sphygmomanometer and a hand-held Doppler. ABI is the ratio of the systolic blood pressure in the ankle to that in the brachial artery. An ABI < 0.9 indicates obstruction, < 0.4 indicates severe ischemia.
• Cultures of deep tissue or curettage of bone should be obtained for most cases (prior to the start of antibiotics). (Strong recommendation).
  • Cultures may not be necessary in cases of a mild infection treated empirically (Strong recommendation).
  • Cultures of superficial swabs should be avoided as their results generally represent colonization rather than infection (Strong recommendation).

Management

• Care should involve a multidisciplinary team, including an infectious disease specialist, a wound care specialist, a podiatrist, an endocrinologist, and a surgeon, when possible.
• Hospitalize all patients with a severe infection, those with a moderate infection, and complications such as peripheral artery disease, or any patient who lacks adequate support to be treated as an outpatient (Strong recommendation).
• Treatment of mild and moderate foot infections without bony involvement involves both wound care and antibiotics.
  • Wound care involves debridement of necrotic tissue, daily dressing changes, and off-loading to reduce pressure on the wound.
  • For mild infections, consider 1-2 weeks of therapy with an oral agent. Selection of a specific agent should be based on the most likely infecting pathogen, with common options including cephalexin 500 mg orally 4 times daily or levofloxacin 500 mg/day orally (Strong recommendation).
  • For moderate-to-severe infections, consider empiric IV antimicrobial therapy based on the probable pathogen followed by pathogen-directed therapy based on culture results and surgical consultation. The duration of therapy depends on the severity and the need for intervention, but often is around 1-4 weeks.
• Consult a vascular surgeon as soon as possible when clinical findings or imaging indicate significant peripheral arterial disease (Strong recommendation).
• For patients with osteomyelitis, the decision to treat medically or surgically is typically individualized based on the severity of infection, surgical risk, and patient preference.
• Before hospital discharge, ensure the patient is clinically stable and has had any urgently needed surgery, achieved acceptable glycemic control, can manage antibiotic and wound care regimens, will adhere to off-loading of wound, and has outpatient follow-up.