Diabetic foot infection

Background

• 75% of patients have polymicrobial infection, usu 70% are gram positive
  • Severe limb/life threatening infection are more likely to involve gram negative aerobic & anaerobic bacteria as well.
  • MRSA is increasing in frequency
• 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

• Cellulitis
• Gangrene
  • Dry gangrene
  • Wet gangrene
• Trench foot
• Abscess
• Necrotizing soft tissue infections
  • Necrotizing fasciitis
  • Necrotizing myositis
  • Necrotizing cellulitis
• Osteomyelitis
• Diabetic foot infection
• Wet-sock erosions

Look A-Likes

• Ingrown toenail
• Peripheral artery disease
• Sporotrichosis
• Deep venous thrombosis

Hyperglycemia

• Physiologic stress response (rarely causes glucose >200 mg/dL)
• Diabetes mellitus (main)
  • Nonketotic hyperglycemia
  • Hyperosmolar hyperglycemic state (HHS/HONC)
  • Diabetic ketoacidosis (adult)
  • Diabetic ketoacidosis (peds)
    • Cerebral edema in DKA
  • Diabetic foot infection
  • Diabetic peripheral neuropathy
• Hemochromatosis
• Iron toxicity
• Sepsis

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

• 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

• 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

• 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

• Clindamycin 450mg PO q8hrs daily x 14 days OR
• TMP/SMX 2DS tabs PO q12hrs daily x 14 days OR
• Doxycycline 100mg PO q12hrs daily x 14 days

Prior antibiotic treatment or moderate infections

• Amoxicillin/Clavulanate 875/125mg PO q12hrs + TMP/SMX 2DS tabs PO q12hrs daily x 14 days OR
• Clindamycin 450mg PO q8hrs + Ciprofloxacin 750mg PO q12hrs x 14 days

Inpatient Treatment

• Vancomycin 15-20mg/kg IV q12hrs plus
  • Ampicillin/Sulbactam 3g IV q6hrs OR
  • Piperacillin/Tazobactam 4.5g IV q8hrs OR
  • Ticarcillin/Clavulanate 3.1g IV q8hrs OR
  • Imipenem 500mg IV q6hrs OR
  • Metronidazole 500mg IV q8hrs PLUS
    • Cefepime 2g IV q12hrs OR
    • Ciprofloxacin 400mg IV q12hrs OR
    • Aztreonam 2g IV q8hrs

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

• Foot diagnoses
• Osteomyelitis
• Neuropathic pain
• Wound care dressing basics