Imaging of the Diabetic Foot

Jim Wu, MD

Beth Israel Deaconess Medical Center Harvard Medical School

Boston, MA

DisclosuresDisclosures

Kaneka Corp - research funding support Boehringer Ingelheim - research funding

support PharmaMar - imaging consultant

Learning ObjectivesLearning Objectives

Learn the imaging exams used to evaluate diabetic foot infection

Learn the strengths and limitations of each imaging test

Learn how to distinguish osteomyelitis from neuroarthropathy (Charcot)

The Diabetic FootThe Diabetic Foot 371 million worldwide with 371 million worldwide with

diabetes (IDF, 2012)diabetes (IDF, 2012) 114 million China, 30 million USA114 million China, 30 million USA

Foot problems occurs in 15-25% Foot problems occurs in 15-25% of patients with diabetes over of patients with diabetes over lifetimelifetime

Foot complications is #1 cause of hospitalization in diabetic patients

Amputations lead to increase morbidity and risk of contralateral amputations (50-60% at 5 years)

Infection in the Diabetic Infection in the Diabetic FootFoot

Due to spread from adjacent ulcer

20% of diabetic foot ulcers will lead to osteomyelitis

Infection can involve the soft tissue or bone

Osteomyelitis and abscess often need surgical treatment

Is it infected?Is it infected?

What are the available imaging What are the available imaging tests?tests?

Radiographs CT Ultrasound Bone scan Leukocyte (WBC) scan MRI PET

American College of Radiology

Both radiographs and MRI should be performed in suspected cases osteomyelitis of the diabetic foot

Bone scan or WBC scan should be use when MRI is contraindicated

When MRI findings are indeterminate (Charcot), bone biopsy is recommended

Last updated in 2008

Radiographs (X rays)Radiographs (X rays)

Strengths: FIRST TEST Cheap, fast, readily available If positive, then good specificity (60-80%) for

osteomyelitis Weaknesses:

Low sensitivity (30-60%) - normal x-ray does not exclude osteomyelitis

Lags clinical symptoms by 1-2 weeks Poor evaluation of soft tissues Difficult to distinguish osteomyelitis from Charcot or

post-op changes

X-rays - OsteomyelitisX-rays - Osteomyelitis

What to look for?

Demineralization Periosteal reaction Bone destruction Soft tissue edema/

blurring of fat plane Gas/air

X-rays - OsteomyelitisX-rays - Osteomyelitis

CTCT Strengths:

Best test for cortical detail Fast exam Soft tissue gas Good for locating sequestra

and sinus tracts

Weaknesses: Poor evaluation of marrow Poor soft tissue detail

without contrast Ionizing radiation

CTCT

UltrasoundUltrasound Strengths:

Good for soft tissues Best test for foreign

bodies! Determine cyst from solid Doppler analysis for

blood flow

Weaknesses: Can’t evaluate bone Need skilled operator

Ultrasound –Foreign BodyUltrasound –Foreign Body

Wood splinter

Bone (Scintigraphy) ScanBone (Scintigraphy) Scan Nuclear medicine study Technetium (99mTc) MDP

(bisphosphonate) is injected intravenously

Radiotracer preferentially accumulates in areas of bone with high turnover Tumors Fractures Arthritis Infection

Strengths: Excellent sensitivity 80-

100% Can look at entire body

Weaknesses: Low/mod specificity 25-60% Poor spatial resolution Can be hard to pinpoint

infection to bone or soft tissues

PITFALL: false negative if poor blood flow

Bone (Scintigraphy) ScanBone (Scintigraphy) Scan

Triple Phase Bone Scan Triple Phase Bone Scan (TPBS)(TPBS)

Phase 1 - Angiographic (1 image/sec, 60 sec) Phase 2 - Blood pool (3-5 minutes after injection) Phase 3 - Delayed (3-4 hrs. after injection)

Phase 4 – Very delayed (24 hours after injection) (patients with poor perfusion, help reduce false negs)

Sensitivity 80-100%, Specificity 25-60%

Triple Phase Bone Scan Triple Phase Bone Scan (TPBS)(TPBS)

Osteomyelitis - positive on all 3 phases

as opposed to

Cellulitis - only 1st 2 phases are positive

Charcot also positive on all 3 phases

Triple Phase Bone Scan Triple Phase Bone Scan (TPBS)(TPBS)

Palestro et al. Semin Nucl Med 39:52-65 © 2009

Angiographic Blood pool Delay

Osteomyelitis of right great toe

Bone Scan - False PositivesBone Scan - False Positives

Tumor Healing fracture Neuroarthropathy (Charcot) Recent surgery Arthritis

Bone scan is sensitive but not specific

Triple Phase Bone Scan Triple Phase Bone Scan (TPBS)(TPBS)

No focal uptake in bone, only soft tissues, consistent with cellulitis

Angiographic Blood pool Delay

No osteomyelitis!!

WBC (Leukocyte) scan

White blood cells (leukocytes) are remove during blood draw, labelled with indium-111, and reinjected back into patient

Tagged leukocytes go to areas of infection

Expensive and more difficult to perform

False positive with areas of red marrow

Good sensitivity (74-86%) and specificity (68-85%)

MRIMRI Strengths:

Excellent marrow and soft tissue detail (guide surgery)

Help distinguish bone versus soft tissue infection

Weaknesses: Not available to all pts

Obese, PM, claustrophobia, hardware

False positives Decrease sensitivity in pts with

ischemia

Sensitivity 90%, Specificity 75-90% Best overall test!!

MRI – OsteomyelitisMRI – Osteomyelitis

What to look for? Dark bone on T1 Bright bone on T2 Marrow enhancement Soft tissue ulcer Sinus tracts Abscesses (rim

enhancement)(give IV contrast if renal function

allows, GFR >30))

T1

T2

dark on T1 bright on T2

MRI – OsteomyelitisMRI – Osteomyelitis

Osteomyelitis with ulcerOsteomyelitis with ulcer

Baker et al. RadioGraphics 2012; 32:1959–1974

T1 T2 T1 post contrast

MRI - BoneMRI - Bone

Very sensitive (90-100%) for detection of osteomyelitis, which is seen as marrow edema

High spatial resolution helps localize pathology High negative predictive value (90-100%)

Normal T1 fat = NO OSTEOMYELITIS

But – marrow edema is non-specific!

Marrow edemaMarrow edema

Avascular necrosis Osteoarthritis Fracture/contusion Recent surgery Tumor Neuropathic arthropathy

MRI – Soft TissueMRI – Soft Tissue

Preferred method for soft tissue imaging Lose normal subcutaneous fat signal

Low T1, High T2, rim enhancement Delineates cellulitis, fistulae, abscesses

Intravenous contrast (gadolinium) helps But – depends on blood flow

Donovan Radiol Clin N AM 2008

MRI - Osteomyelitis with MRI - Osteomyelitis with abscess/fistulaabscess/fistula

T1 T2 T1 post contrast

MRI - Abscess without MRI - Abscess without osteomyelitisosteomyelitis

Donovan et al RadioGraphics 2010; 30:723–736

T1 T2 T1 post contrast

Osteomyelitis diagnosed in 29/29 bones from non-ischemic ulcers

Osteomyelitis diagnosed in only 7/75 bones from ischemic ulcers

Hypothesis – poor blood flow leads to the lack of interstitial edema so MRI can not detect marrow changes

PET scanPET scan 18F-Fluorodeoxyglucose (FDG), an analogue of glucose, is

administered intravenously Radiotracer goes to areas of high intracellular glucose

utilization Activated macrophages, neutrophils, and lymphocytes

Degree of uptake can be quantify by standardized uptake values (SUV) for each scan

Sensitivity 80-100%, Specificity 93% - for diabetic osteomyelitis

PET scanPET scan

Compared to other nuclear medicine scans Shorter study time Higher resolution Higher target-to-background ratio Allows for precise anatomic location Allows for intensity quantification (SUV)

Best for spinal osteomyelitis (since WBC scans are poor)

Evaluation of diabetic foot is not fully clarified

PET/CT - OsteomyelitisPET/CT - Osteomyelitis

Eur J Nucl Med Mol Imaging (2012) 39:1545–1550

FDG uptake (SUVmax 7)

PET/CT – Soft tissue infectionPET/CT – Soft tissue infection

Keidar et al. J Nucl Med. 2005;46:444-449

No uptake in bone excludes osteomyelitis

OsteomyelitisOsteomyelitis

Nawaz et al Mol Imaging Biol (2010) 12:335Y342

MRI PET

Imaging Tests to Evaluate Imaging Tests to Evaluate Diabetic Foot InfectionDiabetic Foot Infection

Radiographs – cheap, first test, not sensitive CT- great cortical detail, see gas well Ultrasound – soft tissue abscesses, FBs Bone scan – very sens not spec, poor detail MRI – BEST OVERALL test for bone and ST WBC scan – hard to do, good sens and spec PET – good test, expensive, potential in

distinguishing charcot from infection

Comparison of Imaging Comparison of Imaging techniquestechniques

Sensitivity Specificity Strengths/weaknesses

Radiographs Low Mod/High cheap and fast

CT Moderate Moderate identifies gas, sequestra

US Low Low better for soft tissue infec

Bone scan High Moderate Poor anatomic detail

WBC scan Moderate Mod/High expensive/time consuming

WBC scan w/ SC High High expensive/time consuming

PET High Mod/High expensive/not billable

MRI with contrast High Mod/High Best anatomic detail

Diabetic Diabetic NeuroarthropathyNeuroarthropathy

Diabetic Neuroarthropathy Diabetic Neuroarthropathy (DN)(DN)

Pathogenesis not completely understood

Repetitive trauma to insensate joints

Autonomic dysfunction of blood flow results in hyperemia and bony resorption

Localized inflammation then leads to bone destruction, joint subluxation and dislocation, and foot deformity

Osteomyelitis, Charcot, or both?Osteomyelitis, Charcot, or both?

Diabetic Neuroarthropathy Diabetic Neuroarthropathy (Charcot) or DN(Charcot) or DN

Can be difficult to distinguish the acute stage of neuroarthropathy from osteomyelitis warm, swollen, erythematous foot

Differentiation is difficult but crucial due to different treatment options Infection requires antibiotics and surgical debridement DN requires offloading and surgical fixation

Sanders and Frykberg – Anatomic Patterns of DN

Patterns 2 and 3 account for 80% cases Ergen et al Diabetic Foot & Ankle 2013, 4: 21884

Diabetic Neuroarthropathy (DN)Diabetic Neuroarthropathy (DN) Imaging

Radiographs Demineralization is first sign Flattening of metatarsal heads Subchondral cysts or periarticular changes in the midfoot with

polyarticular distribution Low sensitivity and specificity in early Charcot

MRI is best for detecting early changes of Charcot Soft tissue edema, joint effusions, subchondral bone marrow

edema of involved joints Low T1, high T2, and marrow enhancement (like infection)

Diabetic Neuroarthropathy Diabetic Neuroarthropathy (DN)(DN)

Imaging Bone scan

Increase uptake in all 3 phases (like with infection) High sensitivity but low specificity

Leukocyte imaging (WBC scan) Better than bone scan as should be negative in Charcot False positive if early phase or rapidly progressing Charcot

PET/CT Small studies suggest may be superior to MRI Lower SUV values correlate with Charcot instead of infection

Eichenholtz Stages of Eichenholtz Stages of CharcotCharcot

Stage 1 - (bone dissolution) damaging acute phase Osteopenia and joint laxity with swollen and erythematous foot

Stage 2 - (coalescence) repair phase Bone debris with osseous fusion or osteosclerosis and reduction in

redness and warmth of the foot

Stage 3 - (remodeling) chronic, healed phase Bony remodeling, fragmentation, collapse of the foot, rocker-bottom

deformity without inflammation

Stage 0 - (clinical signs without X-ray abnormalities) Edema seen on MRI. Treatment ideally begins at this stage

Eichenholtz Stages of Eichenholtz Stages of CharcotCharcot

0

2 4

J Am Acad Orthop Surg September 2009 ; 17:562-571

1

3

Charcot - Stage 0 Charcot - Stage 0

Chantelau et al Swiss Med Wkly. 2013;143:w13831

DN with UlcerDN with Ulcer

Is it infected?Is it infected?

LocationLocation

Neuroarthropathy (Charcot)

LocationLocation

Diabetic osteomyelitis

Osteomyelitis vs. Osteomyelitis vs. Diabetic neuroarthropathyDiabetic neuroarthropathy

Osteomyelitis Forefoot>calcaneus Next to soft tissue ulcers Focal area Erosions Abscesses Bony deformity

uncommon Low T1 and High T2 on

MRI

Neuropathic arthropathy Midfoot Intact skin/soft tissues Periarticular Subchondral cysts No abscesses, small joint

effusions Deformity common with

debris and loose bodies Low T1 and High/Low T2

- Due to sclerosis if low T2

NeuroarthropathyNeuroarthropathy

Chantelau et al Swiss Med Wkly. 2013;143:w13831

Skin is intact!

Diabetic neuroarthropathyDiabetic neuroarthropathy

T1 T2Donovan Radiol Clin N AM 2008

Skin is intact!

Neuroarthropathy with Neuroarthropathy with OsteomyelitisOsteomyelitis

T1 T2Donovan Radiol Clin N AM 2008

Skin is NOT intact!

Neuroarthropathy with Neuroarthropathy with Osteomyelitis and abscessOsteomyelitis and abscess

T1 T2

Donovan Radiol Clin N AM 2008

T1 post contrast

Rim enhancing fluid collection

PET - Osteomyelitis vs PET - Osteomyelitis vs Charcot Charcot

Few studies have using PET to distinguish osteomyelitis from diabetic neuroarthropathy in the diabetic foot

In general DN has lower SUV than osteomyelitis which has lower SUV than DN with osteomyelitis

SUV values:

DN < Osteomyelitis alone < DN+Osteomyelitis

Ahmadi et al Radiology: Volume 238: Number 2—February 2006

PET - Osteomyelitis vs PET - Osteomyelitis vs Charcot Charcot

Osteomyelitis SUV 7.5Nawaz et al Mol Imaging Biol (2010) 12:335Y342

PET - Osteomyelitis vs PET - Osteomyelitis vs Charcot Charcot

Diabetic Neuroarthropathy SUV 1.1 Nawaz et al Mol Imaging Biol (2010) 12:335Y342

Imaging - Future DirectionsImaging - Future Directions

High field strength MRI Higher resolution MR spectroscopy

MRI perfusion imaging IV contrast with dynamic imaging MRA and arterial spin labelling

PET/MRI Limited by the space and MRI compatible PET

scanners

Learning ObjectivesLearning Objectives

Learn the imaging exams used to evaluate diabetic foot infection

Learn the strengths and limitations of each imaging test

Learn how to distinguish osteomyelitis from neuroarthropathy (Charcot)

SummarySummary

X-rays should be the initial exam

MRI is the best exam to evaluate diabetic foot infection for bone and soft tissues

Nuclear medicine scans can be helpful when there are contraindications to MRI

PET/CT is likely the best nuclear medicine test, but unclear if superior to MRI

SummarySummary

Neuroarthropathy can lead to false positive findings for infection on imaging studies

Midfoot location, presence of intact overlying skin, and periarticular involvement can distinguish neuroarthropathy from osteomyelitis

謝謝聆聽