Positron emission tomography/computed tomography: a clinical tool for evaluation of enthesitis in patients with spondyloarthritides

Objective. To evaluate the accuracy of PET/CT using [F-18] fluorodeoxyglucose (FDG) in determining the presence of enthesitis in patients with SpAs. Methods. Results of PET/CT scans of eight patients with SpA and seven patients with RA were retrospectively examined, with specific focus on five joints and three entheses. Volume fixation values are expressed as standardized uptake values (SUVs). Data from 20 patients with non-rheumatic (NR) diseases and 20 healthy subjects were also examined if non-specific, false positive findings were possible. We evaluated the clinical utility of PET/CT examinations in SpA, compared with MRI and Ga scintigraphy. Results. Images of PET/CT scans of the shoulder, hip and knee joints revealed that FDG accumulated at the entheses in SpA and in the synovium in RA patients. The maximum SUVs [mean (S. D.)] were statistically higher in SpA patients compared with RA patients at the entheses of lumbar spinous process [4.83 (1.15) vs 1.42 (0.34); P < 0.05, respectively], pubic symphysis [3.93 (0.87) vs 1.35 (0.31); P < 0.05, respectively] and ischial tuberosity [4.76 (1.5) vs 1.35 (0.42); P < 0.05, respectively]. The positive frequencies of lumbar spinous processes and ischial tuberosity evaluated by PET/CT scan in the SpA group were significantly higher than that evaluated by MRI. Conclusion. MRI is now widely used to detect bone marrow oedema and enthesitis in patients with SpA. PET/CT scans offer an alternative method to identify enthesitis, and will likely contribute to the early diagnosis of SpA.