Diabetic foot infection
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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
- 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
- Trench foot
- Abscess
- Necrotizing soft tissue infections
- Osteomyelitis
- Diabetic foot infection
- Wet-sock erosions
Look A-Likes
Hyperglycemia
- Physiologic stress response (rarely causes glucose >200 mg/dL)
- Diabetes mellitus (main)
- 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)
- Consider vascular consult if abnormal:
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
- 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