Respective Performance of ¹⁸F-FDG PET and Radiolabeled Leukocyte Scintigraphy for the Diagnosis of Prosthetic Valve Endocarditis

Abstract

Echocardiography plays a key role in the diagnosis of infective endocarditis (IE) but can be inconclusive in patients in whom prosthetic valve endocarditis (PVE) is suspected. The incremental diagnostic value of 18 F-FDG PET and radiolabeled leukocyte scintigraphy in IE patients has already been reported. The aim of this study was to compare the respective performance of 18 F-FDG PET and leukocyte scintigraphy for the diagnosis of PVE in 39 patients. Methods: 18 F-FDG PET and leukocyte scintigraphy were performed on 39 consecutive patients admitted because of clinically suspected PVE and inconclusive echocardiography results. The results of 18 F-FDG PET and leukocyte scintigraphy were analyzed separately and retrospectively by experienced physicians masked to the results of the other imaging technique and to patient outcome. The final Duke-Li IE classification was made after a 3-mo follow-up. Results: Of the 39 patients, 14 were classified as having definite IE, 4 as having possible IE, and 21 as not having IE. The average interval between 18 F-FDG PET and leukocyte scintigraphy was 7 ± 7 d. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 93%, 71%, 68%, 94%, and 80%, respectively, for 18 F-FDG PET and 64%, 100%, 100%, 81%, and 86%, respectively, for leukocyte scintigraphy. Discrepancies between the results of 18 F-FDG PET and leukocyte scintigraphy occurred in 12 patients (31%). In patients with definite IE, 5 had true-positive 18 F-FDG PET results but false-negative leukocyte scintigraphy results. Of these 5 patients, 3 had nonpyogenic microorganism IE (Coxiella or Candida). Of patients for whom endocarditis had been excluded, 6 had true-negative leukocyte scintigraphy results but false-positive 18 F-FDG PET results. These 6 patients had been imaged in the first 2 mo after the last cardiac surgery. The last patient with a discrepancy between 18 F-FDG PET and leukocyte scintigraphy was classified as having possible endocarditis and had positive 18 F-FDG PET results and negative leukocyte scintigraphy results. Conclusion: 18 F-FDG PET offers high sensitivity for the detection of active infection in patients with suspected PVE and inconclusive echocardiography results. Leukocyte scintigraphy offers a higher specificity, however, than 18 F-FDG PET for diagnosis of IE and should be considered in cases of inconclusive 18 F-FDG PET findings or in the first 2 mo after cardiac surgery.

Another potential step to improve prosthetic heart valve endocarditis imaging with 18F-FDG PET/CT

“…10 In general, 18 F-FDG PET/CT affords a high sensitivity in the identification of PVE when echocardiographic results are inconclusive. 6,11 Yet, given the pitfalls leading to false-positive findings as described before, 9 the specificity of 18 F-FDG PET/CT in PVE detection may be limited, in particular within the first 2 months after surgical implantation. Albeit early identification of PVE is of utmost importance as these patients have a high mortality when not treated with geared antibiotics in a timely fashion, 12 the low specificity of 18 F-FDG PET/CT in PVE detection may lead to unnecessary surgical re-interventions not without risk.…”

FDG PET/CT in prosthetic heart valve endocarditis: There is no need to wait

“…7 Since then, multiple publications have included patients scanned less than three months (some less than two weeks) after implantation. [8][9][10][11][12][13][14][15] Some explicitly describe true negative findings in scans within this time frame, including our own study in the current issue. 10,12,15 In contrast, a recent study by Mathieu et al which included 51 patients without PVE showed that elevated uptake of FDG in the absence of infection can occur as late as 8 years after implantation, 13 and our own study showed false-positive late images in a patient 13 years after implantation.…”

“…18,19 In cases where FDG PET/CT is difficult to interpret, additional radiolabeled leukocyte scintigraphy may help to further differentiate inflammation from infection: although at the cost of a lower sensitivity, its specificity is higher than that of FDG PET/CT. 8 Finally, it is essential to incorporate all available information in a multidisciplinary approach to establish a final diagnosis. 20 Rather than waiting 3 months to perform FDG PET/ CT in patients with a suspicion of PVE, we should be aware of the variable nature of FDG PET/CT findings in this setting.…”

Modern Opportunities of Radionuclide Methods for Diagnosis of Inflammatory Processes in the Myocardium

“…In a study of Rouzet F. et al a comparison of PET-CT with 18FDG and SPECT-CT with 99 mTc-HMPAOlabeled autoleukocytes for diagnoses of endocarditis was performed, and it was shown that the scintigraphy study had a significantly higher diagnostic efficiency compared to PET [82 ].…”

“…This technique is successfully used to visualize the inflammation of various localizations and has high specificity -from 85% to 96% according to different authors [82,83,84]. At the same time, labeling of leukocytes in vitro, as was mentioned above, involves certain difficulties [50,51].…”