18F-Fluoride PET/CT for detection of sacroiliitis in ankylosing spondylitis

The aim of this study was to evaluate the performance of F-18-fluoride-PET/CT (PET/CT) for the diagnosis of sacroiliac joint (SIJ) arthritis in patients with active ankylosing spondylitis (AS). Included in the study were 15 patients with AS according to the modified New York criteria (AS group) and with active disease and 13 patients with mechanical low back pain (MLBP; control group) who were investigated with whole-body F-18-fluoride PET/CT. The ratio of the uptake in the SIJ and that in the sacrum (SIJ/S) was calculated for every joint. The mean SIJ/S ratio of 30 quantified joints in the AS group was 1.66 (range 1.10-3.07) with PET/CT, and the mean SIJ/S ratio of 26 quantified joints in the MLBP group was 1.12 (range 0.71-1.52). The area under the receiver operating characteristic curve for SIJ arthritis was 0.84. With plain radiography as a the gold standard and taking an SIJ/S ratio of > 1.3 as the threshold, the sensitivity, specificity and accuracy on a per patient basis were 80%, 77% and 79%, respectively. On a per SIJ basis, the greatest sensitivity (94%) was found in grade 3 sacroiliitis (n = 16). Our results suggest that quantitative F-18-fluoride PET/CT may play a role in the diagnosis of sacroiliitis in active AS and is an alternative to conventional bone scintigraphy in times of molybdenum shortage.