Role of 18F-FDG PET/CT in the evaluation of response to antibiotic therapy in patients affected by infectious spondilodiscitis

Aim: The aim of this study is to examine the role of the 18FFDG- PET/CT in patients affected by spondylodiscitis and analyzing new possible parameters to early evaluate therapy response. Materials and Methods: We retrospectively enrolled 61 patients (21 female, mean-age 61) with diagnosis of spondylodiscitis. Among the 61 patients, 11 had tubercular, 1 fungal and 49 pyogenic spondylodiscitis. All patients underwent 18F-FDG-PET/CT baseline scan with determination of C-reactive protein (CRP) value and a second scan after 2-4 weeks of therapy. We analyzed SUVof both scans, delta- SUV (SUV1-SUV2/SUV1) in comparison with CRP levels during therapy. Furthermore we evaluated the volume of the infection, that we named “metabolic infection volume” (MIV) in the first and second scan.We selected a threshold of 50% of Lesion SUV1-2 for MIV definition. Delta-MIV (MIV1-MIV2/ MIV1) were calculated and compared with SUV changes. Lesion-to-liver (LLR) ratio, lesion-to-mediastinal ratio (LBR), delta-LLR and delta- LBR after therapy were evaluated in every patients. Relationship between these different SUV and MIV parameters with therapy response and clinical outcome were investigated. Results: The mean SUVat diagnosis was 9,7+/-3,3. The mean CRP level at diagnosis was 2,9+/-2,8 mg/dl. SUV1 was not correlated with the CRP1 level at diagnosis (p=0.6) and SUV2 was not correlated with CRP2 (p=0.71). In responders patients, SUV2 and CRP2 were significantly lower than SUV1 and CRP1 (p<0.001 and p<0.0001 respectively). MIV2, LLR2 and LBR2 were also significantly lower than MIV1, LLR1 and LBR1 (p<0.003). ROC curves for delta-SUV showed a sensitivity of 87%and a specificity of 82% with a cut-off of 33%. ROC curves for SUV2 showed a