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Diabetic Foot Infections and the Hospitalist

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  • Failure to adequately treat results from knowledge deficits, failure to appropriately allocate resources and insufficient multidisciplinary cooperation.
  • DFI: an inframalleolar infx in a diabetic.
  • Chronic, heavily abt exposed infxs may also feature enterococcus, diphteroids, other non-fermenters. Hospitalization, prior abts may predispose to HA-MRSA (obviously not necessary for CA-MRSA). Foot soaking as a risk factor for Pseudomonas. Recent Falagas review here?
  • CNS, enterococcus, Pseudomonas, diphtheroids can clearly all be pathogenic, but are frequently not. Impaired host defenses in milieu of necrotic ST and bone probably play role in allowing low virulence bugs (CNS, diphtheroids) to become pathogens.
  • Blood cultures in pts systemically ill. Needle aspiration an option for sampling abscesses/purulent collections.
  • Distinction between moderate and severe infections has less to do with the foot, and more to do with “the patient to whom it is attached.” Up to 50% of pts will not show evidence of systemic illness even with severe/limb-threatening infx. Other pts will demonstrate only loss of glycemic control as manifestation of severe dx.
  • Next 3 slides are EMPIRIC regimens.
  • Daptomycin and linezolid 'when MRSA proven or likely.'
  • Vancomycin regimen 'when MRSA proven or likely'.
  • Pus under pressure in foot can rapidly lead to permanent damage. Higher level amputation will sometimes be preferable to lower level amp, if latter unlikely to heal, to leave mechanically unsound foot, or if ulceration recurrent. With regard to ischemia, ABI of 0.5-0.9 suggests mild-mod disease, with wound that should be healable without revasc. Palp DP/PT likewise predict absence of severe ischemia.
  • 75K admits annually in US (ie, OM of feet)
  • Kline A, Internet J of Pod 2007;2:3. Kline A, thefootblog.org.
  • 2-4 week delay in radiographic appearance of OM.
  • Above sens/spec concerns apply to technetium 3-phase. WBC tagged studies improve spec, but at cost of lower sensitivity.
  • Cortical disruption, sinus tract, adjacent ST changes also help to suggest dx.
  • 17 total studies selected. 7 compared bone scan to MRI, 9 compared MRI to plain films. Most studies don't use bone bx as gold standard.
  • Authors conclude MRI clinches dx when other evidence supports OM (PTB, deep ulcer); and also conclude that bone scanning has very limited role in this setting. 2006 Medicare outpt reimbursement for bone scan $288, for MRI of foot with contrast $451.
  • Staph aureus most common isolate in both bone and ulcer cxs. Bone bx appeared safe/well tolerated. 1 pt had acute Charcot foot 4 weeks later, ? relationship. Theoretical concerns with bone bx have included introducing infx, bone fx, failure to heal. Staph aureus and CNS both made up 26% of bone bx + cultures.
  • Some advocate that only necrotic bone (rather than all infected bone) be removed. Game/Jeffcoate series: amputations done either for limb/life-threatening infxs, or non-response to abts. Majority of those treated medically received all-PO regimens, with average duration of Tx 61 days. Importantly, series was consecutive (though retrospective).

Diabetic Foot Infections and the Hospitalist Diabetic Foot Infections and the Hospitalist Presentation Transcript

  • Diabetic Foot Infections and the Hospitalist Jim Pile, MD, FACP Divisions of Hospital Medicine and Infectious Diseases CWRU/MetroHealth Medical Center
  • 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
  • Scope of Diabetic Foot Infections
    • Cellulitis
    • Paronychia
    • Abscess
    • Myositis
    • Infectious tendonitis
    • Septic arthritis
    • Necrotizing fasciitis
    • Osteomyelitis
    • ULCERS
  • 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
  • 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
  • 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)
  • 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
  • Wound Culture
    • Neglected or done incorrectly much of time
    • Don’t 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
  • 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 2004;39:885
  • DFI Staging
    • Uninfected (PEDIS 1)
    • Mild infection (PEDIS 2)
    • - Superficial, cellulitis < 2 cm
    • Moderate infection (PEDIS 3)
    • - Cellulitis > 2 cm, lymphangitis, abscess, gangrene
    • Severe infection (PEDIS 4)
    • - Systemic involvement (fever, hypotension, leukocytosis, severe hypoglycemia, renal failure, etc.)
  • 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
  • Audience Response Question
    • A 44 year old woman with poorly controlled T2DM and a plantar ulcer to the R great toe of > 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 > 400.
  • Audience Response Question
    • Which of the following antibiotic regimens is MOST appropriate?
    • A. Meropenem
    • B. Ciprofloxacin + metronidazole
    • C. Piperacillin-tazobactam + vancomycin
    • D. Clindamycin + levofloxacin
  • 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
  • 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
  • Moderate DFI
    • Trimethoprim-sulfamethoxazole
    • Amox/clavulanate
    • Levofloxacin
    • Cefoxitin
    • Ceftriaxone
    • Amp/sulbactam
    • Linezolid (+/- aztreonam)
    • Daptomycin (+/- aztreonam)
    • Ertapenem
    • Cefuroxime +/- metronidazole
    • Piperacillin/tazobactam
    • FQ + clindamycin
  • Severe DFIs
    • Piperacillin-tazobactam
    • Levofloxacin or ciprofloxacin + clindamycin
    • Imipenem-cilastatin
    • Vancomycin + ceftazidime (+/- metronidazole)
  • 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
  • Goals of Surgery
    • Drainage of pus
    • Correction of severe ischemia
    • Control of infection
    • Salvage of functional foot
    • Surgical expertise varies locally
  • 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
  • Emerging Therapy
    • Hyperbaric oxygen
    • Negative pressure dressings
    • G-CSF
    • Maggot therapy
    • None of above should be a substitute for appropriate antibiotics and surgical therapy
  • 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 > 90
    • Pulse < 100
    • Mental status at baseline
    • -Mandell LA, IDSA/ATS Consensus Guidelines on the Management of CAP in Adults. CID 2007;44:S27-72.
  • 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
  • &quot;Dealing with osteomyelitis is perhaps the most difficult and controversial aspect in the management of diabetic foot infections.&quot; -Lipsky BA. Diagnosis and Treatment of Diabetic Foot Infections. Clin Infect Dis 2004;39:885-910
  •  
  • Suspect Osteomyelitis When . . . .
    • An ulcer is chronic or overlies bone
    • An ulcer fails to heal after ≥ 6 weeks of appropriate treatment
    • A &quot;sausage toe&quot; 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 > 2 cm ²
    • -Lipsky B, CID 2004;39:885; Butalia S, JAMA 2008;299:806
  • 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
  • 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
  • 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/diabeticfoot.
  • 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 1998,23:77
  • 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
  • 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 2007;167:125-132.
  • Kapoor, A. et al. Arch Intern Med 2007;167:125-132.
  • 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 1995;273:721; Shone A, Diab Care 2006;29:945; Lavery L, Diab Care 2007;30:270
  • Probe-to-Bone Characteristics Depend on Prevalence of Osteomyelitis Sens Spec PPV NPV Prev Grayson 66% 85% 89% 56% 66% Shone 38% 91% 53% 85% 20% Lavery 87% 91% 57% 98% 12%
  • 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 2006;42:57
  • 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. &quot;Conservative approach&quot;:
    • --Treat soft tissue infx for 2-4 weeks, then repeat XR
    • B. &quot;Aggressive approach&quot;:
    • --Obtain MRI (or nuclear scan)
  • 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/s00125-008-0976-1
  • Audience Response Question
    • A 53 y.o. diabetic patient is admitted to your service with an erythematous, swollen right 3 rd 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 3 rd toe, and she undergoes ray resection. How long should she be treated with antibiotics post-operatively?
  • 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
  • Duration of Treatment for Diabetic Foot Infections
  • 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