Imaging Assessment of Diabetic Foot Infections Regina Alivisatos, md



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Imaging Assessment of Diabetic Foot Infections

  • Regina Alivisatos, MD

  • Medical Officer

  • DSPIDPs


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



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



Applications to Date



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



Diagnosis - osteomyelitis

  • Presence of osteomyelitis impacts on failure rate of soft tissue infections

  • “gold standard” is bone histology and culture through non-infected tissue



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



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



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%



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



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



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



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



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


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



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



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 1995:196:557-64



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



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



Probe

  • 75 subjects with 76 ulcers from one center

  • Osteomyelitis diagnosed in 50 (66%), excluded in 26

    • 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 1;273(9):721-3



Cost



Conclusion Which procedure?





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