Infectious complications of the diabetic foot
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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 diagnosis meta analysis
Osteomyelitis diagnosis, Meta-analysis

Butalia, et al. JAMA 2008



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


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


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


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