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 w/in 6 mos with optimal care.
• DM 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 joint sprain (turf toe)
• Acute arterial ischemia
• Calcaneal bursitis

Subacute/Chronic

• Diabetic foot infection
• Peripheral artery disease
• Plantar fasciitis
• Trench foot
• Ingrown toenail
• Paronychia
• Tinea pedis
• Morton's neuroma
• Diabetic neuropathy

Hyperglycemia

Diabetic Emergencies

• Diabetic ketoacidosis (DKA)
• Diabetic ketoacidosis (peds)
• Hyperosmolar hyperglycemic state (HHS)
• Nonketotic hyperglycemia
• Euglycemic DKA (SGLT-2 inhibitors, pregnancy, fasting)

Diabetes Mellitus (New or Known)

• Type 1 diabetes mellitus (new-onset or uncontrolled)
• Type 2 diabetes mellitus (new-onset or uncontrolled)
• Medication noncompliance or insulin pump malfunction
• Gestational diabetes
• Latent autoimmune diabetes of adults (LADA)

Medication/Drug-Induced

• Corticosteroids (most common drug-induced cause)
• Thiazide diuretics
• Atypical antipsychotics (olanzapine, clozapine, quetiapine)
• Beta-blockers (especially non-selective)
• Phenytoin
• Tacrolimus, cyclosporine (transplant patients)
• Protease inhibitors (HIV antiretrovirals)
• Catecholamines (epinephrine, norepinephrine infusions)
• SGLT-2 inhibitors (paradoxical DKA with euglycemia)
• Total parenteral nutrition (TPN)
• Dextrose-containing IV fluids (iatrogenic)
• Niacin
• Pentamidine (initially hyperglycemia, then hypoglycemia from beta-cell destruction)

Physiologic Stress Response

• Sepsis / critical illness (stress hyperglycemia — very common in the ED)
• Trauma / major surgery / burns
• Acute coronary syndrome / myocardial infarction
• Stroke (especially hemorrhagic)
• Pancreatitis (both a cause and consequence)
• Shock (any etiology)
• Pain (catecholamine surge)
• Seizure (postictal)
• Physiologic stress alone rarely causes glucose >200 mg/dL in non-diabetics; glucose >200 in a "stress response" should prompt evaluation for undiagnosed diabetes or prediabetes

Endocrine

• Cushing syndrome / Cushing disease (cortisol excess)
• Pheochromocytoma (catecholamine excess)
• Hyperthyroidism / thyroid storm
• Acromegaly (growth hormone excess)
• Glucagonoma (rare)
• Somatostatinoma (rare)

Pancreatic

• Pancreatitis (acute or chronic — destruction of islet cells)
• Pancreatic malignancy (adenocarcinoma, neuroendocrine tumors)
• Post-pancreatectomy
• Cystic fibrosis-related diabetes
• Hemochromatosis (iron deposition in pancreas — "bronze diabetes")

Toxic/Overdose

• Iron toxicity (hepatic injury → impaired glucose regulation)
• Salicylate toxicity (can cause both hyper- and hypoglycemia)
• Sympathomimetic toxicity (cocaine, methamphetamine)
• Calcium channel blocker toxicity (impairs insulin secretion)
• Carbon monoxide toxicity (stress response)

Other

• Renal failure (chronic kidney disease, acute kidney injury — impaired insulin clearance AND insulin resistance)
• Cirrhosis / hepatic failure (impaired glycogenolysis regulation)
• Pregnancy (gestational diabetes, steroid administration for fetal lung maturity)
• Parenteral nutrition (TPN, dextrose-containing fluids)
• Post-transplant diabetes (immunosuppressants)

Complications of Diabetes (Not Causes of Hyperglycemia)

These are associated conditions that may be present alongside hyperglycemia but do not themselves cause elevated glucose:

• Diabetic foot infection
• Diabetic peripheral neuropathy
• Cerebral edema in DKA
• Diabetic retinopathy
• Diabetic nephropathy

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)
• DM 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 DM 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 sx, 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 Rx)
• ESR >40 incr chance of OM 12 fold, an ESR >70 makes dx 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

• Obtain specimens for culture prior tostarting 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