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Infectious complications of the diabetic foot. Bob Pelz, MD PhD. I have no relevant disclosures. Epidemiology. 15% of diabetics develop ulcers, 6% require hospitalizaitons Over half of ulcers become infected 20-66% of infected ulcers involve bone. Spectrum of infections. Cellulitis

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epidemiology
Epidemiology
  • 15% of diabetics develop ulcers, 6% require hospitalizaitons
  • Over half of ulcers become infected
  • 20-66% of infected ulcers involve bone
spectrum of infections
Spectrum of infections
  • Cellulitis
  • Abscess
  • Osteomyelitis
differential diagnosis
Differential diagnosis
  • Non-infected neuropathic ulcer
  • Fracture
  • Ischemia
  • Embolization, vasculitis, stasis ulcer, carcinoma
pathogenesis
Pathogenesis
  • Sensory neuropathy
    • Trauma, deformity
  • Autonomic neuropathy
    • Diminished sweat, dry, cracked skin
  • Hyperglycemia
    • Decreased neutrophil function
  • Arterial disease
challenges in diagnosis of osteomyelitis
Challenges in Diagnosis of Osteomyelitis
  • Neuropathic changes may resemble infection on MRI, other images
  • Superficial cultures correlate poorly with deep organisms, and may not reflect deep infection at all
  • Radiographic signs absent early
  • Bone biopsy invasive, expensive, inaccurate
diagnosis of osteomyelitis
Diagnosis of Osteomyelitis
  • Labs: ESR > 70
  • Radiology
    • MRI, Labeled wbc, plain film
  • Probe to Bone
  • Bone biopsy for histopathology, Cx
  • Surface cultures
  • Wound > 2 cm2
plain radiographs
Plain radiographs
  • Cheap and often very helpful
  • Moth-eaten necrotic bone is dead and requires surgery
probe to bone
Probe-to-bone
  • Grayson, JAMA 1995. 75 inpatients, 66% with osteomyelitis
    • “On gentle probing, the evaluator detected a rock-hard, often gritty structure without the apparent presence of any intervening soft tissue”
    • Gold standard- histo or clinical + radiology
    • Sens/spec/PPV/NPV: 66,85,89,56%
probe to bone1
Probe to Bone
  • Lavery et al (Diab. Care 2007): 247 outpts, 12% with OM.
    • S / S / PPV / NPV=87 / 91 / 57 / 98.
  • Shone, et al Diab Care 2006
    • Sensitivity / Specificity 0.38 / 0.91
  • Aragon-Sanchez, Diab Med 2011 PTB or X ray +. Gold standard = Bx with path showing osteo
    • Sens / Spec 0.97 / 0.92. LR +/- 12.8 / 0.02
    • 85% of those with pos path had pos Cx
  • With exposed bone or positive probe to bone, IDSA guidelines (2004) say X- ray not needed
bone bx
Bone Bx
  • Gold standard in most studies
  • Open Bx more accurate than needle
    • 31 pts, both needle and open (Seneville, CID 2009)
    • 23.9% correlation between open Bx and needle Biopsy Cx
      • Highest with Staph aureus (46.7%)
    • 41.7 correlation between swab Cx and biopsy culture
      • 82.3 for Staph aureus
bone biopsy
Bone Biopsy
  • Weiner (J Foot Ankle Surg 2011) 44 pts with clinical osteo.
    • Just as likely for Bx to be pos by micro as by histo
  • Pos Cx rate low- 34% of 41 histologic osteomyelitis
    • 4 pos Cx in 34 histo-neg pts (Wu et al AJR 2007)
  • White, et al (Radiology 1995) Culture swab sensitivity 42%. 50% of histo-positive Bx had positive Cx
    • Should send Bx specimens for both Cx and histo
superficial cultures pitfalls
Superficial cultures, pitfalls
  • Poorly predictive of deep pathogens
    • 44% of sinus tract Cx contained organism from surg sample (Mackowiak JAMA 1978)
    • 28% concordance, 38% for staph (Zuluaga BMC Infect Dis 2002)
    • Twice as many bacteria species isolated by swab than by Bx (Kessler, Diab Med 2005)
superficial cx advantages
Superficial Cx, advantages
  • Can often choose ABX to cover all plausible organisms
  • Organisms isolated repeatedly and in large numbers likely to be causative
  • Useful for detecting MRSA, other MDRO
  • Staph aureus likely pathogen if found
osteomyelitis treatment
Osteomyelitis Treatment
  • Aerobic GPCs are the predominant pathogens in diabetic foot infections
  • Broad-spectrum empirical therapy is not routinely required but is indicated for severe infections
  • Acute infections are often monomicrobial (almost always with aerobic GPC)

Lipsky et al, CID, 2004

microbiology
Microbiology

Lipsky, et al. CID 2004

antibiotics
Antibiotics
  • Surgery vs abx vs both.
    • ABX can’t sterilize dead bone
  • IV vs po
    • Easier to monitor therapy with IV, especially through RIC or in SNF
    • IV may be preferable if litigious or unreliable pt
    • IV expensive, PICC risks (DVT, infection, etc.)
iv vs po therapy
IV vs PO therapy
  • IV Cloxacillin vs Bactrim/rif, 50 pts with surgical Cx, RCT. (Euba AAC 2009)
    • Relapses no different with 7-9 years f/u
  • Gentry, et al (AAC 1991) Ofloxacin vs IV, Bx-confirmed osteo.
    • 74% vs 86% w/out relapse at 18 month f/u
  • Fleroxacin/rif vs IV: 89% vs. 69% cure (Schrenzel, CID 2004)
  • Ofloxacin/Rif: Diabetic foot Staph. osteo. 76% relapse free at 22 mo. (Senneville CID 2001)
iv vs po therapy1
IV vs PO therapy
  • 9/11 osteo cured with Rif/Linezolid vs 9/10 with Rif/Bactrim (Nguyen Clin Micro Infect 2009). Similar cure with infected hardware.
  • Linezolid vs Unasyn or vanco (MRSA). 45 sites, 8 countries. (Lipsky, CID 2004) Excluded ischemic feet. 371 pts. Cured osteo in 27/44 Linezolid, 11/16 unasyn. More AEs in L arm, but mild
iv vs po therapy2
IV vs PO therapy
  • Generally, cure rates with IV and po therapy comparable. Rifampin almost always given.
duration of therapy
Duration of therapy
  • 4-6 weeks typical, but not based on randomized data
  • IV followed by 3 months po if inadequate debridement
slide30
Case
  • 60, dm, h/o right 4th and 5th ray amputations, retinopathy, neuropathy
  • 4/27/11- Fever, Acute red, tender foot.
    • MRI cuboid edema, ?5th met osteo. No abscess
    • Cx- Group B Strep
    • Keflex 1 week
    • Offloading
slide31
Case
  • 5/10/11 Foot red, 1 week off keflex
    • X ray- no osteo
    • CRP- 0.7
  • 5/24 pus, CRP=9.7, Cx=GBS, faxed in 20 days doxycycline
  • 5/31 erythema better
  • 7/11 Total contact cast
case cont
Case, cont.
  • 8/1/11 Copious drainage, necrotic base, +/- PTB despite total contact cast
    • X ray- still no osteo.
    • Tagged WBC c/w osteo
    • TcPO2 42
case cont1
Case, cont
  • To OR, 8/11/11
    • Path- no osteo, but possible fracture
    • Cx- Proteus, enterococcus
    • 2 weeks keflex
    • Wound improving with resection of weight-bearing 5th metatarsal
    • Wound healed as of 9/11
case summary
Case summary
  • 8 ID, 3 ortho, 13 wound care encounters over 5 months
    • 3 X rays, 1 MRI, 1 bone/WBC scan, TCC, surg
  • Cellulitis, possible abscess, but osteo never definite clinically, probably never had it despite positive cultures.
  • Fracture vs infection
  • Ulcer due to abnormal weight bearing, resolved with surgery
  • Lives with son who is nearly blind
take homes
Take-homes
  • Diagnosis and management of infected foot ulcers difficult, requires team approach
  • Anaerobes, resistant gram negatives not as common as taught. Staph aureus is at least half of infections.
  • Swab Cx, probe to bone, X rays useful
  • Oral therapy likely as good as IV
ad