| |
 |
Download PDF Version of this Article
Bookmark this Site
|
|
Archived Issues of Radiology Rounds
MGH Department of Radiology Website
|
| |
Osteomyelitis and the Diabetic Foot
|
| Note: Updated information available (June 2007) |
| |
- Plain film x-ray should be the first imaging examination for suspected osteomyelitis in the
diabetic foot
- If the initial x-ray is negative, the absence of osteomyelitis can be confirmed by repeat
examination 2-4 weeks later
- MRI can be useful if x-ray images are equivocal or if there is concern for soft tissue infection
- If MRI is not possible, a 99mTc MDP triple phase bone scan can be used to distinguish an
osseous from a soft tissue process but the exam is nonspecific for the diagnosis of infection
|
Diabetic
foot infections are associated with significant morbidity, account for
the largest number of diabetes-related hospital bed days and contribute
to 50% of all lower extremity amputations in the United States. The
annual incidence of foot ulcers in diabetic patients is about 2%,
which, given that there are now 15-20 million diabetics nationally,
extrapolates to over 300,000 cases per year. Approximately 15% of foot
ulcers in diabetics will progress to osteomyelitis, which is much more
difficult to treat than soft tissue infection and greatly increases the
risk of amputation.
Patients who have soft tissue
infections for more than two weeks are at high risk for osteomyelitis.
Osteomyelitis should be considered in any patient with a deep or
extensive ulcer, especially if it is chronic or occurs over a bony
prominence. Osteomyelitis should also be suspected when an ulcer does
not heal after ≥6 weeks of appropriate care and off-loading, if bone is
visible, or can be palpated by a sterile blunt probe. Other symptoms
suggestive of osteomyelitis in a diabetic include foot or toe swelling
in a patient with a history of foot ulceration, unexplained high WBC
count or other inflammatory markers, or hyperglycemia.
| Clinical Indications of Osteomyelitis |
| Osteomyelitis should be considered if: |
| - |
Deep or extensive ulcer, especially if chronic or over bony prominence |
| Osteomyelitis should be suspected if: |
| - |
Unhealed ulcer after ≥6 weeks medical care and off-loading |
| - |
Visible bone |
| - |
Bone palpable with a probe |
| Other symptoms suggestive of osteomyelitis |
| - |
Foot or toe swelling with history of ulceration |
| - |
Unexplained elevated WBC count or other markers of inflammation
|
A definitive diagnosis of osteomyelitis is made with bone biopsy and
subsequent examination by histology and microbiology. But this invasive
procedure is not always advisable for patients with advanced vascular
disease or Charcot arthropathy due to difficulty with healing and
nonspecific inflammatory changes, respectively. Consequently, imaging
is often used as an aid to diagnosis.
|
|
|
|
| |
| Figure 1. Radiographic
image of a diabetic patient who previously underwent a transmetatarsal
amputation shows lucency in the distal fifth metatarsal (arrow),
suggestive of osteomyelitis. |
Standard Plain Film Radiography
Radiographs are important for initial patient evaluation and are
diagnostic when cortical bone abnormalities characteristic of
osteomyelitis are seen, such as cortical erosion, periosteal reaction,
and lucency or osteolysis. However, these abnormalities may not be
apparent until 7-15 days after the onset of acute clinical
osteomyelitis and the early subtle changes are not easily
differentiated from those due to Charcot osteoarthropathy.
Consequently, the sensitivity and specificity of initial x-ray
examinations are low.
If an initial x-ray examination of a diabetic patient with suspected
osteomyelitis is negative, a follow up examination should be performed
2-4 weeks later. If the imaging findings are unchanged, then it is
likely that the infection is confined to soft tissue. A positive
diagnosis of osteomyelitis can be made if the characteristic cortical
abnormalities are seen. If the radiographic findings are equivocal,
i.e. consistent with but not diagnostic of osteomyelitis, further
imaging examinations can be considered.
|
 |
| |
| Figure 2.
MR images of same patient. A. T1-weighted image showing decreased bone
marrow signal (arrows), due to edema consistent with osteomyelitis and
B. T2-weighted image of the same patient showing increased signal from
bone marrow (arrow), cutaneous ulcer (arrowhead), and a soft tissue
collection (dashed arrow). |
|
|
MRI
Of the alternate imaging examinations for osteomyelitis, MRI has been
shown to be most useful because it can reliably detect primary bone
marrow abnormalities and secondary abnormalities including cortical
bone destruction, cellulitis, phlegmon, abscess, and sinus tracts. The
primary findings of osteomyelitis are decreased signal on T1 weighted
images, increased signal on T2 weighted images, and enhancement
following contrast administration in the bone marrow. However, the
indicators with the highest positive predictive value for osteomyelitis
are the secondary findings of cortical bone interruption, cutaneous
ulcer, and a sinus tract adjacent to areas of bone marrow signal
abnormality. In the absence of these specific criteria, false
positive diagnoses of osteomyelitis may occur due to similarity of the
imaging findings of osteomyelitis to those of reactive bone marrow,
neuropathic arthropathy or stress reaction. These conditions are
especially common in diabetics and can coexist with osteomyelitis,
further complicating the ability to obtain an accurate diagnosis.
| Range of Reported Sensitivity and Specificity of Imaging Methods for the Diagnosis of Osteomyelitis |
| Imaging Exam |
Sensitivity |
Specificity |
| Plain film X-ray |
60%(28-93) |
66%(50-92) |
99mTc three phase bone
|
70-90% |
38-79% |
111In Oxyquinolone WBC
|
80-100% |
70-90% |
| MRI* |
88-99% |
83% |
| *Highest and lowest values excluded |
|
|
| |
| Figure 3. Image of the same patient from third phase of 99mTc-MDP bone scan, showing increased uptake of radioactivity (arrow) in fifth metatarsal bone. |
|
|
Nuclear Medicine Studies
If an MRI is not possible, nuclear medicine offers several
alternatives. The most commonly used nuclear medicine examination is
the three phase bone scan. This consists of a "perfusion" phase
(obtained during injection of the tracer), which shows hyperemia, an
"equilibrium" phase (obtained about one minute after injection of
tracer), which shows soft tissue abnormalities, and a "delayed" phase
(obtained about 2-3 hours after injection), which is specific for bone
abnormalities. Acute osteomyelitis typically appears as abnormalities
on all three phases of the scan while soft tissue infections without
bone involvement (e.g. cellulitis without osteomyelitis) will appear
abnormal on the first two phases. Degenerative and other chronic bone
changes will appear as abnormalities only on the third phase.
Although very sensitive for osteomyelitis, the three phase scan loses
specificity in the setting of recent trauma or surgery since either of
these will mimic osteomyelitis. In addition, Charcot foot also displays
abnormalities in all three phases of the bone scan and can be confused
with osteomyelitis. The two conditions can sometimes be
differentiated by the more generalized joint involvement in Charcot’s
neuropathy and by the clinical scenario.
An alternative nuclear imaging technique is the 111In-labeled
white blood cell scan. Although this examination is sensitive to the
presence of infection, image resolution is poor and often fails to
distinguish whether the infection is in bone, soft tissue, or
both. A combined approach using labeled white blood cells and a
standard bone scan of the area of concern demonstrates similar imaging
sensitivity and specificity to MRI; however, this usually requires two
visits by the patient, one for injection and a second visit, 24 hours
later, for imaging.
Scheduling
Radiology examinations may be ordered through ROE (http://mghroe
)
or by telephone 617-724-XRAY (9729) for all locations. Radiography is
performed at the MGH Main Campus, Mass General West Imaging Waltham,
MGH Charlestown Health Center, MGH Chelsea Health Center, and MGH
Revere Health Center. MRI is performed Mass General West Imaging -
Waltham, Mass General Imaging - Charlestown, and Mass General Imaging -
Chelsea. Nuclear imaging is performed at the MGH Main Campus and Mass
General West Imaging Waltham.
Further Information
For further questions, please contact Kevin Hoover, M.D., Ph.D.
, Musculoskeletal Radiology, 617-724-4255.
We would like to thank Dr. Hoover as well as Daniel I Rosenthal, M.D.,
Erik Nelson, M.D., and Miriam Bredella, M.D., Musculoskeletal
Radiology, James A. Scott, Nuclear Medicine, and Enrico Cagliero, M.D.,
Diabetes Unit, Department of Medicine, for their assistance and advice
for this issue.
|
| |
|
This article provided useful information about the appropriate use of imaging studies:
Note: clicking one of these options will close this window. |
References
|
|
Collins, MS, Schaar, MM, Wenger, DE and Mandrekar, JN. (2005) T1-weighted MRI characteristics of pedal osteomyelitis. AJR Am J Roentgenol 185: 386-93
Lipsky, BA, Berendt, AR, Deery, HG, Embil, JM, Joseph, WS, Karchmer,
AW, LeFrock, JL, Lew, DP, Mader, JT, Norden, C and Tan, JS. (2004) Diagnosis and treatment of diabetic foot infections. Clin Infect Dis 39: 885-910
Ramsey, SD, Newton, K, Blough, D, McCulloch, DK, Sandhu, N, Reiber, GE and Wagner, EH. (1999) Incidence, outcomes, and cost of foot ulcers in patients with diabetes. Diabetes Care 22: 382-7
Schinabeck, MK and Johnson, JL. (2005) Osteomyelitis in diabetic foot ulcers. Prompt diagnosis can avert amputation. Postgrad Med. 118: 11-5
Turpin, S and Lambert, R. (2001) Role of scintigraphy in musculoskeletal and spinal infections. Radiol Clin North Am 39: 169-89
|
|
|
|
|
|
|
|
