Is FDG-PET A Better Imaging Option For Diabetic Osteomyelitis?

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Author(s): 
Hope C. Markowitz, BA, Harley B. Kantor, BA, Randy Cohen, DPM, and Khurram H. Khan, DPM

   De Winter and colleagues performed a prospective study using FDG-PET scans on 60 patients suspected of having chronic infections involving the axial and appendicular skeleton.8 Two experienced, unbiased radiologists read the scans independently. The final diagnosis was based on histology and bacterial cultures in 18 patients and clinical findings with a minimum follow-up of six months in 42 patients.

   The researchers determined that 25 patients were infected with osteomyelitis being identified correctly by both radiologists.8 There were four false positives. The sensitivity for the group with appendicular skeletal infections was 100 percent and the specificity was 86 percent. These authors determined that the PET scan is highly accurate at diagnosing chronic osteomyelitis and could become the standard imaging technique for this condition.

   Basu and co-workers conducted a prospective clinical trial comparing the use of PET scan to MRI in diabetic feet complicated by acute Charcot neuroarthropathy.9 The authors wanted to discover if PET could distinguish between Charcot osteoarthropathy and osteomyelitis. The patients were divided into four groups: 17 patients with Charcot neuroarthropathy, 21 patients with uncomplicated diabetic feet, 20 non-diabetic patients with normal lower extremities and five patients with osteomyelitis secondary to complicated diabetic feet.

   Even in the presence of Charcot and coexisting foot ulcers, the PET scan accurately ruled out osteomyelitis.9 Charcot joints had small amounts of diffuse uptake of FDG. The PET had 100 percent sensitivity and 93.8 percent accuracy in the diagnosis of Charcot foot in this study. In contrast, MRI was 76.9 percent sensitive and 75 percent accurate.

   In their meta-analysis comparing different imaging modalities for the diagnosis of chronic osteomyelitis, Termaat and colleagues concluded that FDG-PET had the highest accuracy in confirming or excluding the diagnosis of chronic osteomyelitis with a pooled sensitivity of 96 percent and a pooled specificity of 91 percent.5 However, they noted that due to the limited availability of PET, one can use combined bone and leukocyte scintigraphy with satisfactory accuracy to diagnose chronic osteomyelitis in the appendicular skeleton.

Exploring The Specific Advantages Of FDG-PET

In comparison to other nuclear imaging modalities, FDG-PET has the advantage of being able to provide results within two hours.10 Bone scans stay positive for a long time after a fracture but the uptake of FDG usually normalizes after two to three months following a fracture, making it useful in evaluating chronic osteomyelitis with previous trauma.2,11,12

   In comparison to imaging modalities such as CT, MRI and ultrasound, FDG-PET is advantageous because it offers full body coverage, high sensitivity, an absence of artifacts from metallic hardware and a lack of reactions to pharmaceuticals.2 Unlike WBC scans, FTG-PET is highly sensitive for osteomyelitis in patients who have taken antibiotics before imaging.13

   While it is well documented that hyperglycemia can adversely affect FTG-PET scan results when physicians use them to detect neoplasms, Zhuang and co-workers concluded that mild to moderate hyperglycemia (<250 mg/dl) does not appear to adversely affect the results when one uses the scan to detect inflammation.14

   The disadvantages of FDG-PET include its limited availability and high cost.5 Additionally, 18F-FDG has a half-life that is not very long (110 minutes) so one must schedule patients very strategically throughout the day.15

How Combining FDG-PET With CT Scans Can Provide Enhanced Results

Another issue with FDG-PET is the fact that it has a comparably low spatial resolution when one measures this against other techniques such as CT. Fortunately, physicians can overcome this with the combined modality FDG-PET/CT.16

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