99mTc-Ciprofloxacin planar and tomographic imaging for the diagnosis of infection in the postoperative spine: experience in 48 patients

The non-invasive assessment of postoperative spinal infections can pose a substantial diagnostic challenge, especially in the presence of orthopaedic devices. Whereas white blood cell scanning is of limited use in the spine, the low normal bone marrow uptake of technetium-99m ciprofloxacin combined with its claimed bacterial specificity makes it theoretically an ideal candidate for the evaluation of postoperative spinal infections. This study aimed to evaluate 99mTc-ciprofloxacin planar and single-photon emission tomography (SPET) imaging in relation to microbiological and clinical diagnosis in the postoperative spine. Planar imaging was performed at 1, 3 and 24 h and SPET was performed at 3 h post injection of 370 MBq 99mTc-ciprofloxacin. Images were scored by two independent certified nuclear medicine physicians, blinded to the final diagnosis. Within the 48 patients, there were 13 deep infections. Sensitivity, specificity and accuracy at visual scoring were respectively 54%, 71% and 67% (1 h), 62%, 77% and 73% (3 h), 42%, 91% and 77% (24 h) for planar imaging and 100%, 74% and 81% for SPET. When recently operated patients (< 6 months) were excluded, the specificity of the SPET imaging rose to 81%. In conclusion, unlike white blood cell scanning, 99mTc-ciprofloxacin SPET is sensitive in evaluating infections in the postoperative spine. Sensitivity is much higher for SPET than for planar imaging. However, the results presented prove that its specificity is limited, especially in recently operated patients. Taking this limitation into account, we advise planar and SPET imaging at 3 h post injection and an interval of at least 6 months after surgery to minimise the likelihood of false positives.

18-Fluorine fluorodeoxyglucose positron emission tomography for the diagnosis of infection in the postoperative spine

BACKGROUND

Using conventional imaging methods, including magnetic resonance imaging and labeled leukocyte scanning, the diagnosis of infection in the postoperative spine remains a diagnostic challenge. Recently, promising results have been reported using 18F-fluorodeoxyglucose positron emission tomography for various infectious problems. This study aimed to investigate the value of 18F-fluorodeoxyglucose positron emission tomography in patients suspected of having spinal infection after previous surgery of the spine.

METHODS

Fifty-seven consecutive patients with a history of previous spinal surgery were prospectively included between February 1999 and June 2001. 18F-fluorodeoxyglucose positron emission tomography was performed 60 to 90 minutes after injection of 370 MBq 18F-fluorodeoxyglucose. Images were scored visually and semiquantitatively by two blinded, independent, certified nuclear medicine physicians, experienced with positron emission tomography. Differences were assessed by consensus. Results were correlated with final diagnosis allowing calculation of sensitivity, specificity and accuracy. Receiver operating characteristic analysis was performed to find optimal cut-off values.

RESULTS

Fifteen patients had spinal infection. Using the most sensitive cut-off values sensitivity, specificity and accuracy were 100%, 81%, and 86%, respectively, for both visual and semiquantitative scoring. In the group without metallic implants (n = 27), false positives (n = 2) only occurred in the first 6 months after surgery. In the group with metallic implants (n = 30), false positives (n = 6) were not confined to recently operated patients.

CONCLUSIONS

Overall accuracy was excellent (86%) with a negative predictive value of 100%. 18F-fluorodeoxyglucose positron emission tomography holds promise to become the standard imaging technique in this difficult patient population, as it is straightforward, provides a rapid result (2 hours) and because accurate alternatives are lacking.