LAUSR

Dear Sir, We thank Dr. Suarez Fernandez for his comment and questions [1] regarding our consensus document for the diagnosis of prosthetic joint infection (PJI), which was prepared as a set of multidisciplinary guidelines by delegates of four European Societies and agreed by the board members of these four societies: the European Association of Nuclear Medicine (EANM), the European Bone and Joint Infection Society (EBJIS), the European Society of Radiology (ESR) and the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) [2, 3]. Dr. Suarez Fernandez expressed his disagreement with some of the data and recommendations included in this guideline. The first comment is about statement 19 of the consensus document: “F-FDG-PET in patients with suspected PJI has high sensitivity but lower specificity than white blood cell (WBC) scintigraphy or anti-granulocyte antibody scintigraphy”. Here, we performed a systematic review on the use of F-FDG-PET in patients with suspected PJI and the comparison with WBC scintigraphy. We agree completely that there are only a few good comparison studies available and that most studies were performed on out-dated camera systems, and in heterogeneous patient groups without a clear definition of PJI. We shared here also the results of a previous guideline published in 2013 where a sensitivity of 95% and a specificity of 98% for knee and hip PJI were reported [4]. We just mentioned this paper as one of the 15 papers in this field and did not go into depth about the details of the analysis that was performed in this guideline leading to these percentages, but we also mentioned that there is discordance between several studies and reviews leading to a large range in sensitivity (28– 91%) and specificity (34–97%) between all studies. It all depends on which interpretation criteria and which devices were used, and we all know that there is no agreement on which interpretation criteria are the best for the use of F-FDG-PET in PJI. For WBC scintigraphy, this is much more standardized the last years [5] and we can rely on the high mentioned diagnostic accuracies (> 90%) in several publications with this technique when using the correct acquisition and interpretation criteria [6–8]. The second comment is concerning the proposed flowchart for the use of nuclear medicine examinations in PJI. Here, FFDG-PET is recommended as an alternative to three-phase bone scan when the time after the prosthesis implant is more than 2 years, since F-FDG-PET has a high sensitivity like bone scan. In our opinion, F-FDG-PET can be used as a rule-out technique in patients with low probability for PJI as an alternative for bone scintigraphy. With both techniques, it is possible to completely exclude a PJI in case of negativity. On the other hand, costs and availability should be considered. Dr. Suarez Fernandez thinks this affirmation is inaccurate. Indeed, in most of the cases, there is always to some degree FDG uptake visible, due to reactive inflammation around the metallic implant or due to reaction to loosening [9]; bone scintigraphy is easier to perform in most centres and is cheaper, so we fully agree that in clinical practice bone scan will be preferred by many clinicians and imagers above FFDG-PET for this indication. However, we want to point out that this consensus document was written as an “evidencebased” guideline and not an “expert opinion” guideline. And, indeed, several papers were published suggesting a role This article is part of the Topical Collection on Infection and Inflammation