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Infectious complications of the diabetic foot

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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Infectious complications of the diabetic foot

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  1. Infectious complications of the diabetic foot Bob Pelz, MD PhD

  2. I have no relevant disclosures

  3. Epidemiology • 15% of diabetics develop ulcers, 6% require hospitalizaitons • Over half of ulcers become infected • 20-66% of infected ulcers involve bone

  4. Spectrum of infections • Cellulitis • Abscess • Osteomyelitis

  5. Differential diagnosis • Non-infected neuropathic ulcer • Fracture • Ischemia • Embolization, vasculitis, stasis ulcer, carcinoma

  6. Evaluation overview

  7. Pathogenesis • Sensory neuropathy • Trauma, deformity • Autonomic neuropathy • Diminished sweat, dry, cracked skin • Hyperglycemia • Decreased neutrophil function • Arterial disease

  8. Pathogenesis

  9. 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

  10. 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

  11. Plain radiographs • Cheap and often very helpful • Moth-eaten necrotic bone is dead and requires surgery

  12. 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%

  13. 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

  14. 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

  15. 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

  16. 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)

  17. 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

  18. Osteomyelitis diagnosis, Meta-analysis Butalia, et al. JAMA 2008

  19. Osteomyelitis diagnosis, Meta-analysis Dinh, MT, CID 2008

  20. 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

  21. Microbiology Lipsky, et al. CID 2004

  22. 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.)

  23. IV Antibiotics, MRSA

  24. IV Antibiotics, MSSA

  25. Oral antibiotics

  26. 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)

  27. 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

  28. IV vs PO therapy • Generally, cure rates with IV and po therapy comparable. Rifampin almost always given.

  29. Duration of therapy • 4-6 weeks typical, but not based on randomized data • IV followed by 3 months po if inadequate debridement

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

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