Roundtable Insights On Imaging For Foot And Ankle Wounds

Volume 18 - Issue 5 - May 2005
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Other Key Points On Nuclear Medicine Leukocyte Imaging

When using nuclear medicine leukocyte imaging (NMLI), Molly Judge, DPM, says it is critical to use this imaging prior to any surgical manipulation of soft tissue, muscle, bone or joint.

Surgical manipulation distorts normal anatomic compartments, changes local anatomy and, most importantly, causes direct tissue damage that can mimic infection when using some NMLI techniques, according to Dr. Judge.

NMLI techniques such as 99mTc-HMPAO, combination imaging with 99mTc-MDP and Indium-labeled leukocytes and Neutrospec imaging are “all viable methods for pre-surgical assessment of chronic wounds.”

When treating noncompliant patients, Dr. Judge says NMLI can be particularly useful in ruling out indolent infection. Using NMLI can help document if there is no infection at the time of treatment, according to Dr. Judge. She adds that this can help counter any potential argument of misdiagnosis or delayed diagnosis in the event of limb loss despite the best of efforts.

She adds that the radiologist’s reading of NMLI is an important aspect of medical/legal documentation.

“If there is any unusual area of positivity in the extremity, there will be a caution in the radiologist’s report suggesting that this may represent an infectious process,” notes Dr. Judge.

When it comes to osteomyelitis (as shown above), there are a variety of imaging techniques one can use to help confirm the diagnosis, according to Thomas Zgonis, DPM. (Photo courtesy of Robert Snyder, DPM)

Here is a radiograph that reveals osteomyelitis. In regard to an initial radiolucency, Dr. Zgonis says underlying osteomyelitis requires five to seven days to manifest radiographically. (Photo courtesy of Lawrence Karlock, DPM)

This MRI STIR technique identifies the region of a loculated abscess formation that rests immediately beneath the remnant of cuboid bone. Note the intermedullary edema indicated by the increased signal intensity within the adjacent osseous structures of t

As one can see, the 99mTc-MDP study reveals the extent of degenerative bone in a “burned out” Charcot foot while the indium 24-hour image fails to reveal a focus of infection in that same patient with Charcot neuroarthropathy. (Photos courtesy of Molly Ju

Roundtable Insights On Imaging For Foot And Ankle Wounds

Author(s):

Clinical Editor: Lawrence Karlock, DPM

He notes that he tends to rely more upon clinical findings, lab and microbiology studies, and standard X-rays. However, when there is no exposed bone in the wound, Dr. Ford says he will use nuclear medicine imaging more as the specificity for osteomyelitis would be greater.

Dr. Zgonis does order scintigraphy to confirm osteomyelitis as well as to determine its extent. Technetium-99 bone scans can be positive for numerous conditions including but not limited to osteomyelitis, Charcot neuropathy, fractures, systemic arthritides, bone tumors and postsurgical changes, according to Dr. Zgonis. While these scans are not “very specific,” he notes they are “quite sensitive” in diagnosing osteomyelitis. Dr. Zgonis adds that the literature supports the use of more specific tests including but not limited to Gallium-67, Indium-111, Tec-99 HMPAO and sulfur colloid scans in confirming osteomyelitis.^4,5

Nuclear medicine imaging (NMI) does play “a very distinct role” in managing diabetic wounds, according to Dr. Judge. When considering any unusual wounds or chronic wounds that seem to be getting worse despite meticulous local wound care, Dr. Judge pursues ancillary imaging to detect the underlying culprit.

Through extensive use of NMLI in her clinical practice, Dr. Judge has found NMLI to be “extremely helpful in identifying the entire spectrum of disease from malignancy to infection.”

Using Neutrospec, one of the newer agents on the market, Dr. Judge says one can perform the imaging within a few hours after injection. She says the monoclonal antibody imaging agent is easy to obtain and given its ability to create an in vivo leukocyte label, it is “the technique of choice for many cases in wound care management.”

Q: What role does MRI play in the treatment of lower-extremity wounds?

A: Drs. Ford and Zgonis agree that MRI is valuable in determining the presence of soft tissue versus bone infection as well as the extent of the involvement. Dr. Zgonis adds that MRI is a “great tool” when there is ulcer or osteomyelitis involvement in the forefoot and the patient has no Charcot destructive changes. With advances in technique and interpretation, Dr. Ford says specialized MRI is “probably the most accurate and useful test other than biopsy.”

However, Drs. Zgonis and Ford also sound a few cautionary notes. Postsurgical changes, Charcot neuroarthropathy, trauma, fractures and avascular necrosis may generate false positives, according to Dr. Zgonis. He also notes that MRI results can be difficult to interpret when there is a coexisting Charcot deformity with an underlying bone or soft tissue infection.⁶

Given issues of cost and potential “overkill” with MRI, Dr. Ford notes that he reserves the imaging modality for difficult and inconclusive cases.

While Dr. Judge uses MRI very frequently when it comes to managing musculoskeletal pathology, she says MRI can be problematic with chronic wounds.

When assessing patients with chronic wounds, Dr. Judge cautions that there is often a biomechanical shift as the patient is offloading the wound. This results in the patient modifying his or her gait and ambulation, and shifting weight onto other uninvolved regions of the foot and ankle. As a result of this weight shift, Dr. Judge says it is very common for a MRI to reveal an increased intramedullary edema in bone, which in and of itself can confound the interpretation of the exam. In this case, she says one may “overzealously” interpret the extent of the infection.