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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