Imaging Assessment of Diabetic Foot Infections

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Imaging Assessment of Diabetic Foot Infections

• Regina Alivisatos, MD
• Medical Officer
• DSPIDPs

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Introduction

• Patients with osteomyelitis should be identified
• in order to ensure
• the most appropriate course of treatment
• a homogenous clinical trials population
• 7 14 of enrolled subjects found to have
• osteomyelitis
• excluded from the PP populations
• failures in the ITT analysis

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WHY?

• Decreasing size of the PP populations that may be
  distributed unequally
• Inaccurate assessment of the true efficacy for
  one or both of the treatment arms
• Database size insufficient to draw conclusions
  about a drugs efficacy in CSST infections or in
  the diabetic foot subset

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Applications to Date
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Complications

• Determination of infection complicated because of
  superimposed neuropathic osteoarthropathy and
  peripheral vascular disease
• Neuropathic disease can lead to f/x, deformity,
  bone production, and hyperemia which can mimic
  infection on MRI and scanning increasing the
  false positives
• Peripheral vascular disease can prevent contrast
  material or tracer from reaching site of concern
  and lead to false negatives

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Diagnosis - osteomyelitis

• Presence of osteomyelitis impacts on failure rate
  of soft tissue infections
• gold standard is bone histology and culture
  through non-infected tissue

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Procedures

• 1) Plain films
• 2) Radionuclide or Scintigraphic imaging
• Triple Phase Bone Scan (TPBS)
• Gallium Scan
• Indium-111 Leukocyte Scan
• 3) Magnetic Resonance Imaging (MRI)
• 4) Probe to Bone

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Procedures

• 1) Plain films
• 2) Radionuclide or Scintigraphic imaging
• Triple Phase Bone Scan (TPBS)
• Gallium Scan
• Indium-111 Leukocyte Scan
• 3) Magnetic Resonance Imaging (MRI)
• 4) Probe to Bone

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X-Ray

• Initial screening tool
• Easily obtained, relatively inexpensive and
  provides anatomical information
• Demineralization, periosteal reaction, bony
  destruction (the classic triad)
• Appear after 30 50 of bone destroyed and can
  take as much as 2 weeks to appear
• Found in other conditions such as fracture or
  deformity
• Sensitivity and specificity approximately 54 and
  80

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Procedures

• 1) Plain films
• 2) Radionuclide or Scintigraphic imaging
• Triple Phase Bone Scan (TPBS)
• Gallium Scan
• Indium-111 Leukocyte Scan
• 3) Magnetic Resonance Imaging (MRI)
• 4) Probe to Bone

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Three-phase bone scintigraphy (TPBS)

• Highly sensitive since positive as early as 24
  hours after onset
• Focal hyperperfusion, hyperemia, bony uptake
• Can also be seen in fractures, neuropathic joints
  and longstanding cellulitis decreasing
  specificity
• Fourth phase (24 hour image) enhances specificity
• Concurrent TPBS with IN111 scanning optimal

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TPBS

• Literature review of 20 reports of 1,166 patients
  (method of confirmation of osteomyelitis
  diagnosis not specified)
• In patients w/o prior bone changes 94 sensitive
  and 85 specific for osteomyelitis
• In patients with complicating conditions 95
  sensitive, 33 specific.
• Schauwecker et al The scintigraphic
  diagnosis of osteomyelitis. AJR 1992 158(1)9-18

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Gallium Scanning

• Must be performed with a TPBS
• Diagnostic criteria include
• gallium uptake exceeds TPBS scan uptake
• gallium and TPBS scan results are discordant
• Sensitivity 81 and specificity 69
• Cost of gallium scan AND TPBS may exceed cost of
  a single more sensitive and specific test such as
  an Indium scan or an MRI
• Schauwecker et al. AJR 158 9 - 18,
  January 1992

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Indium scanning

• Best sensitivity, specificity, and cost
  compromise in patients with and without prior
  bone abnormalities
• Issue of practicality of labeling WBCs and later
  images
• Does not accumulate at sites that are not
  infected
• Compilation of sensitivity and specificity for
  142 diabetic subjects from 5 studies showed
  sensitivity of 88.6 and specificity of 84
• Schauwecker et al. AJR 158 9 - 18, January 1992

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Procedures

• 1) Plain films
• 2) Radionuclide or Scintigraphic imaging
• Triple Phase Bone Scan (TPBS)
• Gallium Scan
• Indium-111 Leukocyte Scan
• 3) Magnetic Resonance Imaging (MRI)
• 4) Probe to Bone

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MRI High-tech, high cost?

• Decreased marrow signal intensity on T1-weighted
  images and increased signal intensity on
  T2-wighted images with marrow enhancement after
  injection of contrast
• Associated findings of soft tissue mass, cortical
  destruction, sequestrum formation and sinus
  tracts with ulceration increase diagnostic
  certainty
• Good anatomical detail
• Sensitivity and specificity comparable to that of
  Indium scan
• Review of 129 diabetics showed MRI sensitivity of
  86 and specificity of 84
• American College of Radiology Imaging
  diagnosis of Osteomyelitis in patients with
  DM/Appropriateness Criteria, 1999

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MRI continued

• 62 feet in 59 patients with suspected
  osteomyelitis were prospectively evaluated (27
  with DM, 35 w/o)
• In DM sensitivity 82, specificity 80
• In non-DM sensitivity 89, specificity 94
• Accuracy increased with contrast-enhanced studies
  (89) vs.78
• Cost savings initially because test is more rapid
• Competitively priced compared with combination of
  TPBS and Indium or with gallium
• Allows good delineation of surgical field
• Morrison, WB et al, Radiology Aug
  1995196557-64

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TPBS with In-111-labeled WBC scintigraphy in the
examination of the feet in diabetic patients
Results of Published Reports
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Procedures

• 1) Plain films
• 2) Radionuclide or Scintigraphic imaging
• Triple Phase Bone Scan (TPBS)
• Gallium Scan
• Indium-111 Leukocyte Scan
• 3) Magnetic Resonance Imaging (MRI)
• 4) Probe to Bone

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Probe

• 75 subjects with 76 ulcers from one center
• Osteomyelitis diagnosed in 50 (66), excluded in
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• Confirmation based on histologic examination
• culture data not analyzed as cultures were taken
  from base of infected ulcer
• if bone biopsy not done, diagnosis was based on
  radiographic tests or surgeons finding of
  purulent nonviable bone
• Bone probed in 36 of 50 with contiguous
  osteomyelitis and in 4 of 26 w/o osteomyelitis
• Sensitivity 66, specificity 85, positive
  predictive value 89, negative 56
• Conclusion Palpation of bone strongly correlated
  with presence osteo. Probing included in initial
  assessment of diabetics with infected ulcers.
  Specialized imaging studies not necessary if
  positive
• Grayson et al JAMA 1995 Mar 1273(9)721-3

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Cost
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ConclusionWhich procedure?