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
  • Severe limb/life threatening infection are more likely to involve gram negative aerobic & anaerobic bacteria as well.
  • MRSA is increasing in frequency
• 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 diagnoses

Acute

• Foot and toe fractures
• Subtalar dislocation
• Metatarsophalangeal sprain (turf toe)
• Acute arterial ischemia
• Calcaneal bursitis

Subacute/Chronic

• Diabetic foot infection
• Peripheral artery disease
• Plantar fasciitis
• Trench foot
• Ingrown toenail
• Tinea pedis

Hyperglycemia

• Diabetic foot infection
• Diabetic ketoacidosis (DKA)
• Diabetic ketoacidosis (peds)
  • Cerebral edema in DKA
• Hemochromatosis
• Hyperosmolar hyperglycemic state (HONC)
• Iron toxicity
• New onset diabetes mellitus
  • Diabetic peripheral neuropathy
• Nonketotic hyperglycemia
• Sepsis

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

• 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

• 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

See Also

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

References

Authors

Ross Donaldson