Diabetic Foot Infections and the Hospitalist

1
Diabetic Foot Infections and the Hospitalist

• Jim Pile, MD, FACP
• Divisions of Hospital Medicine and Infectious
  Diseases
• CWRU/MetroHealth Medical Center

2
The Problem

• Diabetic foot infections are common, expensive
  and probably increasing in frequency
• The most frequent reason for hospitalization in
  diabetic patients
• The most common reason for amputations
• Current treatment often fails to conform to
  available evidence/guidelines

3
Scope of Diabetic Foot Infections

• Cellulitis
• Paronychia
• Abscess
• Myositis

• Infectious tendonitis
• Septic arthritis
• Necrotizing fasciitis
• Osteomyelitis
• ULCERS

4
Risk Factors for Diabetic Foot Ulceration and
Infection

• Sensory neuropathy
• Motor neuropathy
• Autonomic neuropathy
• Neuro-osteoarthropathic deformities (eg Charcot)
• Peripheral vascular disease

• Hyperglycemia
• Host factors
• Patient non-adherence
• Sub-optimal care by health care system

5
Audience Response Question

• Treatment of cellulitis in the patient with
  longstanding diabetes should include coverage of
• A. Gram positive organisms
• B. Gram positive and negative organisms
• C. Gram positives and anaerobes
• D. All of the above

6
Microbiology of Diabetic Foot Infections

• Gram positive organisms predominate, especially
  in acute wounds
• --Staph aureus
• --B-hemolytic strep (especially groups A and B)
• Chronic wounds and/or recent antibiotics
• --Enterobacteriaceae (and gram positives)
• Chronic, heavily treated infections
• --Coag neg Staph, Pseudomonas, anaerobes (
  above)

7
Microbiology of DFIs

• Polymicrobial wounds typically demonstrate 3-5
  pathogens on culture
• Significance of all of these often unclear,
  however
• Limb (and life) threatening infections should be
  assumed to be polymicrobial until proven otherwise

8
Wound Culture

• Neglected or done incorrectly much of time
• Dont culture uninfected ulcers!
• Failure to debride wound before culture a common
  mistake
• Tissue from debrided ulcer base provides optimal
  material for culture
• But swab from debrided ulcer also acceptable

9
Staging Severity of Infection

• Staging classification adopted by International
  Consensus on Diabetic Foot and IDSA utilizes
  PEDIS acronym
• -P perfusion
• -E extent/size
• -D depth/tissue loss
• -I infection
• -S sensation
• -Lipsky B, Clin Infect Dis 200439885

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DFI Staging

• Uninfected (PEDIS 1)
• Mild infection (PEDIS 2)
• -Superficial, cellulitis lt 2 cm
• Moderate infection (PEDIS 3)
• -Cellulitis gt 2 cm, lymphangitis, abscess,
  gangrene
• Severe infection (PEDIS 4)
• -Systemic involvement (fever, hypotension,
  leukocytosis, severe hypoglycemia, renal
  failure, etc.)

11
Admission Criteria

• Essentially all patients with severe infection,
  and some with moderate, require hospitalization
• Most patients with mild infection may be treated
  as outpatients

• Reasons for admission
• -Systemic toxicity
• -Severe metabolic disturbances
• -Rapid progression
• -Critical ischemia
• -Unable to care for self
• -Need for urgent diagnostic or therapeutic
  interventions

12
Audience Response Question

• A 44 year old woman with poorly controlled T2DM
  and a plantar ulcer to the R great toe of gt 1
  month duration presents with several days of
  progressive pain, erythema and swelling of the
  foot. Tc is 38.4 C, her WBC is 14K and her BS
  is gt 400.

13
Audience Response Question

• Which of the following antibiotic regimens is
  MOST appropriate?
• A. Meropenem
• B. Ciprofloxacin metronidazole
• C. Piperacillin-tazobactam vancomycin
• D. Clindamycin levofloxacin

14
Antibiotic Therapy

• Does the patient need antibiotics?
• Choice of agent will be dictated by severity of
  infection as well as chronicity
• Difficult to make definitive recommendations
  based on available data

15
Mild Diabetic Foot Infections

• Dicloxacillin
• Clindamycin
• Cephalexin
• Trimethoprim-Sulfamethoxazole
• Levofloxacin

• How does progressive emergence of CA-MRSA affect
  these recommendations?
• Ideal regimen will reliably cover CA-MRSA and
  B-hemolytic Strep

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Moderate DFI

• Trimethoprim-sulfamethoxazole
• Amox/clavulanate
• Levofloxacin
• Cefoxitin
• Ceftriaxone
• Amp/sulbactam

• Linezolid (/- aztreonam)
• Daptomycin (/- aztreonam)
• Ertapenem
• Cefuroxime /- metronidazole
• Piperacillin/tazobactam
• FQ clindamycin

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Severe DFIs

• Piperacillin-tazobactam
• Levofloxacin or ciprofloxacin clindamycin
• Imipenem-cilastatin
• Vancomycin ceftazidime (/- metronidazole)

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Surgical Indications

• Urgent
• -Gas gangrene
• -Necrotizing fasciitis
• -Compartment syndrome
• -Critical ischemia

• Other indications
• -Abscess
• -Progressive infection despite antibiotics
• -Unexplained foot pain
• -Need for ulcer debridement

19
Goals of Surgery

• Drainage of pus
• Correction of severe ischemia
• Control of infection
• Salvage of functional foot
• Surgical expertise varies locally

20
Important Adjuncts to Ulcer Healing

• Off-loading
• -Mechanical stress on ulcerated area MUST be
  prevented
• -Bedrest, crutches, surgical/half shoes,
  removable cast walker, etc.
• Debridement
• -Sharp debridement generally preferable
• Appropriate dressing
• -Moist wound environment promotes
  epithelialization
• -Many commercial products available, none
  clearly superior

21
Emerging Therapy

• Hyperbaric oxygen
• Negative pressure dressings
• G-CSF
• Maggot therapy
• None of above should be a substitute for
  appropriate antibiotics and surgical therapy

22
Discharge Criteria

• No evidence-based criteria exist
• Extrapolating from community-acquired pneumonia
  literature, as a minimum the following should be
  met

• T 37.8 C
• Blood pressure gt 90
• Pulse lt 100
• Mental status at baseline
• -Mandell LA, IDSA/ATS Consensus Guidelines on
  the Management of CAP in Adults. CID
  200744S27-72.

23
Discharge Criteria

• Adequate glycemic control should be present
• Any immediately necessary surgery should be
  accomplished
• Clear wound care and off-loading plans should be
  outlined and clear to patient
• Definitive antibiotic regimen selected
• Site of care, follow-up appointments and
  communication with PCP

24
"Dealing with osteomyelitis is perhaps the
most difficult and controversial aspect in the
management of diabetic foot infections."-Lipsky
BA. Diagnosis and Treatment of Diabetic Foot
Infections. Clin Infect Dis 200439885-910
25
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Suspect Osteomyelitis When . . . .

• An ulcer is chronic or overlies bone
• An ulcer fails to heal after 6 weeks of
  appropriate treatment
• A "sausage toe" is present
• A swollen foot is present with a history of foot
  ulceration

• An ulcer is accompanied by otherwise unexplained
  elevated ESR/CRP
• Bone is visible or can be probed in an ulcer base
• Any ulcer that is deep or extensive
• Ulcer area is gt 2 cm²
• -Lipsky B, CID 200439885 Butalia S, JAMA
  2008299806

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Audience Response Question

• The single BEST test for the diagnosis of
  osteomyelitis in the diabetic foot is
• A. WBC-tagged nuclear scan
• B. Positive probe-to-bone test
• C. MRI
• D. FDG-PET

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Osteomyelitis of the Foot Diagnostic Challenges

• Distinction between soft tissue and OM (or
  uninfected ulcer and OM) frequently unclear
• Changes on plain XR delayed and inconsistent
• Lab values don't provide resolution between OM
  and STI
• Neuro-osteoarthropathy (Charcot) may mimic OM
• Advanced imaging is expensive

29
Plain Films

• Simple and cheap
• Radiographic changes lag clinical pathology
• Recent review found sensitivity/specificity
  61/72
• Probably underutilized
• -Learch T, Advanced Imaging of the Diabetic Foot
  and its Complications. www.gentili.net/diabeticfoo
  t.

30
Nuclear Medicine Imaging

• Sensitivity is high
• Relatively expensive
• Time consuming
• Specificity is problematic
• WBC-tagged scans may be helpful in distinguishing
  Charcot arthropathy from OM
• -Lipman B, Clin Nucl Med 1998,2377

31
MRI

• Focal decrease in marrow signal on T1-weighted
  and increase on fat-suppressed T2-weighted images
  suggests diagnosis of osteomyelitis
• Sensitivity high
• Much more specific than nuclear studies
• Expense suggests MRI may be over-utilized in this
  setting

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MRI vs. Other Imaging Modalities

• Recent meta-analysis found that at sensitivity of
  90, specificity of MRI for foot osteomyelitis
  was 83
• MRI markedly better than nuclear studies or plain
  films
• DOR 150 vs. 3.6 for MRI vs. bone scan
• DOR 82 vs. 3.3 for MRI vs. plain films
• - Kapoor, A. et al. Arch Intern Med
  2007167125-132.

33
Kapoor, A. et al. Arch Intern Med
2007167125-132.
34
Probe-to-Bone Test

• Bedside test touted as low-tech means of
  diagnosis
• Positive predictive value reported as 89
• Recent studies suggest caution with generalizing
  these results
• -Grayson M, JAMA 1995273721 Shone A, Diab
  Care 200629945 Lavery L, Diab Care 200730270

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Probe-to-Bone Characteristics Depend on
Prevalence of Osteomyelitis
36
Bone Biopsy

• 76 patients with 81 episodes of DFO confirmed by
  bone biopsy
• 69 cases had ulcer swab cultures as well
• Bone biopsy isolates 77 gram , 18 gram
  negative, 5 anaerobes
• Bone/ulcer cxs concordant in 17
• 70 of ulcer cxs did not grow bone pathogen(s)
• -Senneville E, Clin Infect Dis 20064257

37
IDSA Guidelines Approach to Suspected Diabetic
Foot OM

• 1. Begin with plain films of foot
• -If c/w osteomyelitis, treat as such
• 2. If plain films not suggestive of osteomyelitis
• A. "Conservative approach"
• --Treat soft tissue infx for 2-4 weeks, then
  repeat XR
• B. "Aggressive approach"
• --Obtain MRI (or nuclear scan)

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Osteomyelitis Medical vs. Surgical Treatment

• Traditional thinking mandates resection of
  infected bone
• Even limited amputations may adversely affect
  foot mechanics, setting up vicious cycle
• Slowly mounting evidence that many cases of
  diabetic foot OM respond to antibiotics alone
• Recent study of 147 pts found 77 treated
  medically, with good result in 82 of these
• -Game FL, Diabetologia DOI 10.1007/s00125-008-09
  76-1

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Audience Response Question

• A 53 y.o. diabetic patient is admitted to your
  service with an erythematous, swollen right 3rd
  toe and forefoot cellulitis. The toe infection
  appears to have been prompted by a plantar ulcer
  of several weeks duration. An MRI strongly
  suggests osteomyelitis of the proximal and distal
  phalanges of the 3rd toe, and she undergoes ray
  resection. How long should she be treated with
  antibiotics post-operatively?

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ARS (continued)

• A. She doesn't require additional antibiotics,
  the non-viable bone has been removed
• B. 7-10 days
• C. 2-4 weeks
• D. 4-6 weeks

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Duration of Treatment for Diabetic Foot
Infections
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Summary

• The microbiology of DFIs is at least somewhat
  predictable, based on chronicity and antibiotic
  exposure
• Cultures should be obtained from the base of a
  debrided ulcer
• Many cases of diabetic foot osteomyelitis can be
  treated based on plain films alone
• All tests are fallible, but MRI offers the best
  combination of sensitivity and specificity