Prolonged back pain attributed to suspected spondylodiscitis. The value of ¹⁸F-FDG PET/CT imaging in the diagnostic work-up of patients.

OBJECTIVE: This study aimed at investigating the diagnostic value of ¹⁸F-FDG PET/CT in cases of suspected spondylodiscitis after inconclusive results in initial diagnostic imaging.

PATIENTS, METHODS: We analysed 38 consecutive cases of suspected spondylodiscitis (mean age: 67 ± 14 years) with chronic back pain referred to our Department during a four-year-period after inconclusive results in MRI or other conventional modalities. Clinical histories were retrospectively worked up and results of ¹⁸F-FDG PET/CT and MRI were analysed and related to the results of biopsy, blood culture and a one-year clinical follow-up. ¹⁸F-FDG PET/CT was analysed qualitatively by visual analysis and quantitatively. We measured the maximum standardized uptake value (SUV(max)) in the region of back pain and in a corresponding reference region (RR) in each patient and calculated a SUV(max-ratio).

RESULTS: 22/38 patients had confirmed spondylodiscitis, while 16 were negative. ¹⁸F-FDG PET/CT established a correct diagnosis in 34 out of 38 patients by visual analysis. ¹⁸F-FDG PET/CT reached a sensitivity, specificity and accuracy of 81.8%, 100%, 89.5% and a PPV and NPV of 100% and 80%. MRI, performed in 27 patients reached a sensitivity, specificity and accuracy of 75%, 71.4%, 74.1% and a PPV and NPV of 88.2% and 50%. Patients with confirmed spondylodiscitis showed a significantly (p < 0.05) higher SUV(max) of 5.1 ± 1.9 and SUV(max)-ratio of 1.9 ± 0.8 than patients without it (SUV(max) (3.8 ± 1.5), SUV(max-ratio) (1.2 ± 0.3).

CONCLUSION: ¹⁸F-FDG PET/CT provided diagnostic information in most patients with chronic back pain and suspected spondylodiscitis. It was helpful in establishing a correct diagnosis in challenging cases of spondylodiscitis with mostly unclear findings in previous MRI.