TO THE EDITOR:
We have read with interest the letters by Das et al. (1) and Pauwels et al. (2) regarding the characteristics of 99mTc-ciprofloxacin imaging for detection of infections. The above correspondence cites our previous work, and the latter group was “surprised to hear that only 40% specificity was obtained using scintigraphic data after 4 h, because this information has never been included in reports by the London group and puts a different complexion on the reliability of previously published clinical data.”
We would like to correct the inaccuracy in referring to our original data (3). Our work shows that in patients with hip prosthesis infections, the specificity of 99mTc-ciprofloxacin imaging was 41% at 1-h imaging, 68% at 4-h imaging, and 95% at 24-h imaging—for a sensitivity of 100%. Our data are thus in good agreement with previously published clinical data, and the citation of a 41% specificity after 4 h may have inspired Pauwels et al. to a more subjective interpretation than one allowed by the results of our original study.
REPLY:
We read with interest the letter by Larikka et al. referring to our reply to a letter to the editor (1,2). In this reply, we expressed our surprise when Das et al., referring to data by Larikka et al. (3), mentioned “an increase in specificity from 41% to 95% when a 24-h image was combined with a 4-h image… . ” From the present letter by Larikka et al., we understand that the real specificity at 4 h amounts to 68% instead of 41% as reported by Das et al., who cited the work in the wrong way and put us on the wrong track. Therefore, we appreciated that Das et al., in an erratum published 2 mo after the publication of our reply, corrected their inaccuracy (1). Nevertheless, also in the abstract by Larikka et al., this information was not clearly stated since it is written “In 13 (59%) of the non-infected patients, non-specific uptake of 99mTc ciprofloxacin was found in the 1-h and 4-h images, which disappeared, however, in the 24-h images.” The data of Larikka et al. are in full agreement with our preclinical observations at early intervals of injection of radiolabeled ciprofloxacin. Indeed, their and our studies pointed out that 99mTc-ciprofloxacin cannot discriminate between infectious and sterile inflammatory processes at 1 h after injection of the tracer. Although Larikka et al. demonstrated an improved accuracy of 99mTc-ciprofloxacin with extended imaging time, in our experiments there was no need to improve any diagnostic accuracy with late images since 99mTc-labeled antimicrobial peptides were already able to distinguish infections from sterile inflammations 1 h after injection of the tracer (4). It should be realized that in our experiments, ciprofloxacin was used as a control, as stated before (4). Lastly, could Dr. Larikka and colleagues (including Britton as coauthor (3)) demonstrate where we made a “subjective interpretation”? In their letter, they did not provide evidence for this.
