Is FDG-PET A Better Imaging Option For Diabetic Osteomyelitis?
Making an accurate diagnosis of osteomyelitis in a patient with diabetes is essential in order to minimize complications. Nearly 33 percent of diabetic foot infections develop osteomyelitis. Most of these infections are a result of direct contiguous spread from soft tissue lesions.1
Early diagnosis and antibiotic therapy are important in order to prevent amputation. In healthy patients, acute osteomyelitis does not usually present a diagnostic challenge. This is due to the obvious systemic signs and symptoms such as fever, malaise, pain, tenderness and decreased motion of affected bone.2 However, in diabetic patients with acute osteomyelitis, the common signs and symptoms of infection are often absent.3
In distinguishing chronic osteomyelitis from acute osteomyelitis, Schauwecker noted that chronic osteomyelitis involves greater than one episode of treatment and/or a persistent infection lasting more than six weeks.4 The diagnosis of chronic osteomyelitis is often difficult to make utilizing radiological and nuclear imaging studies since there can be preexisting changes in the osseous architecture from prior trauma or surgery.2
Many published studies have detailed the accuracy of the numerous modalities physicians currently use to diagnose osteomyelitis.5 These modalities include radiography, computed tomography (CT), magnetic resonance imaging (MRI), leukocyte scintigraphy, bone scintigraphy, gallium scintigraphy and combined techniques. The most recent modality is fluorodeoxyglucose positron emission tomography (FDG-PET).
In terms of diagnostic studies, the best imaging modality is one that is both highly sensitive and specific. Several studies have recently reviewed FDG-PET for its ability to diagnose osteomyelitis accurately.2 The results indicate that FDG-PET may be the most sensitive and specific imaging modality currently available to determine the presence or absence of osteomyelitis. Most importantly for podiatrists, it may be more helpful than other modalities in differentiating Charcot neuroarthropathy from osteomyelitis in patients with diabetes.
Assessing The Accuracy Of Current Imaging Modalities
Dinh and colleagues performed a meta-analysis to determine the pooled sensitivity and specificity of radiography, MRI, bone scan and leukocyte scan for the diagnosis of osteomyelitis.6 They found that the pooled sensitivity for radiography was 54 percent and pooled specificity was 68 percent. Changes on radiographs were not evident until 40 to 70 percent of the bone had been resorbed, reducing the sensitivity in the initial two to four weeks of the infection. Pooled sensitivity for MRI was 90 percent and pooled specificity was 79 percent. Pooled sensitivity for bone scan was 81 percent and pooled specificity was 28 percent. Pooled sensitivity for leukocyte scan was 74 percent and pooled specificity was 68 percent.
In their meta-analysis, Termaat and co-workers found that a combined bone and leukocyte scan has a pooled sensitivity of 78 percent and a pooled specificity of 84 percent.5 Out of the aforementioned modalities, researchers found that MRI was the most accurate at diagnosing osteomyelitis.6,7
Comparing FDG-PET To Other Imaging Modalities
The 18F-fluorodeoxyglucose (FDG) is a radiolabeled glucose analog. The FDG-PET was originally in use for the diagnosis of neoplastic disorders but has now expanded to include the diagnosis of different inflammatory conditions. There is an increased uptake of FDG in activated inflammatory cells like macrophages and lymphocytes. This is caused by significantly increased levels of glycolysis due to an increase in
the number of cell surface glucose transporters from cytokine cell stimulation.2 Various studies have assessed the accuracy of the FDG-PET at diagnosing osteomyelitis.