4/8/2017 NONE Alexander Reyzelman DPM, FACFAS - Co-Director, UCSF - - PowerPoint PPT Presentation

4/8/2017 1 Alexander Reyzelman DPM, FACFAS

• Co-Director, UCSF Center for Limb Preservation
• Associate Professor, Dept of Medicine

California School of Podiatric Medicine at Samuel Merritt University

NONE

MRI Marrow edema

Decreased signal on

T1

Increased signal on

T2

Abscesses, sequestra,

sinus tracts

Sensitivity – 90-99% Specificity – 60-80% Marrow: decreased signal intensity on T1-w images:

• Geographic, medullary distribution, confluent =
• steomyelitis

T1 T2 FSE fatsat

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Marrow: decreased signal intensity on T1-w

and increased signal intensity on T2-w,

Enhancement with intravenous gadolinium

(Gd) – but not if ischemic due to PAD

IV gadolinium (Gd): improves detection of soft

tissue abscess, sinus tracts and devitalized tissue (+/- for diagnosis of osteomyelitis)

Short axis T1 with gadolinium with

• steomyelitis of second metatarsal

68 y.o. male DM x 30 yrs

with history of healed right hallux IPJ ulcer

Reports recurrent

redness and swelling of the hallux and has had several courses of oral ABX during the past 3 months

States that his right

hallux and foot gets recurrent swelling and redness after he finishes the course of ABX

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WBC- 9.8 Afebrile ESR – 4 CRP – 2.2 Xrays:

• 1. Cortical collapse and irregularity with possible

erosion of the lateral aspect of the articular surface of the first metatarsal head with increasing sclerosis is concerning for osteomyelitis given the clinical history of cellulitis. Posttraumatic change or

• steonecrosis may also be considered. MRI may be

helpful for further evaluation.

60-80% Many conditions can

cause marrow edema

Inflammation of

adjacent tissues may result in inflammation

• f the bone

Presence of Charcot

makes it even more problematic

90-100% Early osteomyelitis

characterized by marrow edema associated with inflammation

Vartanians et al. Skel Rad 2009

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Acute neuropathic osteoarthropathy Acute fracture Stress fracture Recent surgery Altered weight-bearing Arthritis Reactive marrow edema

Post- Gd Infected Non-infected Subchondral cysts 2% 76% Joint erosion 51% 39% Diffuse marrow involvement T1-weighted 41% 12% T2-weighted 48% 12% Post-gadolinium 42% 9%

Ahmadi ME et al: Radiology 2006;238:622-631.

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Infected Non-infected Joint effusion:

Thin rim enhancement

21% 62%

Diffuse enhancement

47% 26% Soft tissue fluid collection 95% 48% Replacement of subcut. fat 68% 36% Sinus tract 84% 0%

Ahmadi ME et al: Radiology 2006; 238:622-631.

MRI is the best imaging modality for

diagnosing osteomyelitis

Sensitivity of >90% Specificity of around 80% Positive Predictive Value = 84%

• With a Pre-test probability of 50%

The probability of disease prior to

testing

• Patient’s history (duration of the ulcer, lack of

treatment response)

• Objective findings (size of the ulcer, probing to

bone)

• Simple diagnostic test (Xrays, ESR)

Kapoor et al. Arch In Med 2007

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Large/extensive ulceration Deep ulceration Ulceration Overlying bony prominences Ulceration that fails to heal with standard

treatment

Biochemical markers (ESR, CRP) Radiographs showing bone destruction

Acute Ulceration Shallow Ulceration Cellulitis without Ulceration Rapid Improvement/Healing Lack of Bony deformity Low ESR Probe to Bone Exposed Bone Radiographic Bone destruction Multiple Risk Factors Chronic Ulceration Deep Ulceration Extensive Ulceration Overlying Bony Structures Recurrent Infection Slow/Stalled healing High ESR LOW MODERATE HIGH

Patient Evaluation

Low ESR -4 Low CRP- 2.2 No ulcer Not probing LOW PRE TEST

PROBABILITY

PPV= 36%

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Negative MRI does a good job of ruling out osteomyelitis Positive MRI should be interpreted with extreme caution. Accuracy of MRI in distinguishing osteomyelitis vs.

Charcot has not been established in the general population

• f diabetic patients with low prevalence of infection

Interpretation of a positive MRI should be done in

conjunction with other objective findings.

As with most other diagnostic tests, the predictive value is

heavily influenced by the underlying prevalence of the disease.

“Most clinicians agree that MRI is the most

useful of the clinical imaging tools”

17 studies evaluating imaging of pedal

• steomyelitis in diabetics: 55% pre-test

probability of disease - PPV of MRI = 84%

With 10% pre-test probability of disease:

would yield 36% PPV of MRI

Conclusion: selection bias may over-value a

diagnostic test

*Vartanians VM et al: Skeletal Radiol 2009;38:633.