Roundtable Insights On Imaging For Foot And Ankle Wounds

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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
Roundtable Insights On Imaging For Foot And Ankle Wounds
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Author(s): 
Clinical Editor: Lawrence Karlock, DPM

   Dr. Zgonis says one should employ this test in the assessment of all acute and chronic foot ulcers that appear infected. He adds that this test may “obviate further advanced imaging to confirm the diagnosis of osteomyelitis.” Probing to bone and the presence of clinical and systemic signs of infection are “still the most reliable indicators of underlying osteomyelitis,” according to Dr. Zgonis.

   Dr. Judge concurs that a chronic wound that probes to bone is particularly concerning as it may be a harbinger of impending osteomyelitis. When there is a negative X-ray in the presence of an open wound that probes to bone, Dr. Ford says either the bone is not infected or the bone is infected but just has not shown up on X-rays yet.

   In regard to the initial radiolucency, Dr. Zgonis says underlying osteomyelitis requires five to seven days to manifest radiographically. He adds that it takes between 10 to 14 days for the first signs of sequestrum and involucrum to be noticeable.

   Dr. Zgonis says one can use radiographs to determine the presence of soft tissue swelling, ulcer tracking, gas in the tissues, cortical irregularity and focal demineralization.2 When it comes to an early presentation of osteomyelitis, Dr. Zgonis notes that initial radiographs are usually abnormal in less than 5 percent of the patients. Yet by the third or fourth week, 90 percent of the patients will demonstrate clinical changes consistent with osteomyelitis.3

   In the particular clinical scenario raised above, Dr. Judge says the lack of radiographic changes in bone would make her suspect an indolent soft tissue infection. When it comes to determining whether there is a microbial cause for treatment failure, Dr. Judge proceeds to use nuclear medicine leukocyte imaging (NMLI).

   She says NMLI results will reveal one of three things. The results may indicate an infection and provide specifics on the location and extent of the infection. The results can identify when no infection exists and accordingly support the continued use of conservative care including second opinions. One can also use NMLI to diagnose a coincident inflammatory process similar to what one might see in the presence of hypertrophic bone or malignancy.

   In addition to identifying and localizing an infectious process, Dr. Judge says using NMLI can help one delineate between bone and soft tissue infection.

   Usually, if there is infected soft tissue and one can probe to bone, one is dealing with osteomyelitis, according to Dr. Ford. If the wound is not infected, Dr. Ford emphasizes obtaining a biopsy and culture of the exposed bone to determine whether the patient has osteomyelitis, and treating the patient accordingly based upon the results.

   Q: What role do nuclear medicine studies play in the treatment of diabetic wounds?

   A: Dr. Ford says the results can be “confusing due to the suspicion of false positives and false negatives.” He rarely finds nuclear medicine studies helpful in managing wounds. When there is exposed bone through a chronic wound on the plantar aspect of the foot, Dr. Ford points out that bony turnover is likely and a response of inflammatory cells will make it “extremely difficult” to distinguish between infection and inflammation.

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