Imaging Assessment of Diabetic Foot Infections Regina Alivisatos, md

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?