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Abstract
OBJECTIVE. We aimed to evaluate the pharmacokinetics and maximum standardized uptake value (SUVmax) of 18F-NaF PET/CT for assessment of disease activity and prediction of response in patients with ankylosing spondylitis (AS). MATERIALS AND METHODS. Twenty-seven patients (age, interquartile range, 30.25-49.75 years) with AS who were receiving a tumor necrosis factor-α (TNF-α) blocker were included. All patients underwent dynamic PET of the pelvis followed by whole-body PET/CT. Quantitative analysis of kinetic data of the sacroiliac joints (SIJs) was performed, and the SUVmax of the SIJs and SUVmax of the spine were calculated. Clinical indexes related to AS disease activity (serum C-reactive protein level, Bath ankylosing spondylitis disease activity index [ BASDAI], and Bath ankylosing spondylitis functional index) were evaluated. Clinical response was defined as an improvement from the initial BASDAI score of 50% or more (BASDAI 50) within 2 years after baseline 18F-NaF PET/CT. RESULTS. The BASDAI score at 18F-NaF PET/CT was significantly different between the responders and nonresponders: 18F-NaF uptake at the spine was significantly higher in the responders than in the nonresponders. Only SUVmax of the spine had a significant positive correlation with BASDAI score at PET/CT (r = 0.38, p = 0.048). The BASDAI score at PET/CT (odds ratio [OR], 35.32; 95% CI, 2.09-57.84; p = 0.014) and SUVmax of the spine (OR, 14.69; 95% CI, 0.79-27.27; p = 0.027) were significantly associated with BASDAI 50 response prediction. CONCLUSION. The results of our study suggest that the SUVmax of the spine on whole-body 18F-NaF PET/CT is a reliable and noninvasive biomarker for predicting therapeutic response to TNF-α blocker and shows better performance for predicting response than quantitative pharmacokinetic parameters. Fluorine-18-labeled NaF PET/CT showed axial bone lesions with bone formation and can be used as a monitoring tool in patients with AS receiving anti-TNF-α drugs. However, these results need to be validated in a larger cohort.

Affiliations

Keunyoung Kim  1 , Seung Min Son  2 , Tae Sik Goh  3 , Kyoungjune Pak  1 , In-Joo Kim  1 , Jung Sub Lee  3 , Seong-Jang Kim  4   5   6
1 Department of Nuclear Medicine, BioMedical Research Institute, Pusan National University Hospital, Busan, Republic of Korea.
2 Department of Orthopaedic Surgery, Pusan National University Yangsan Hospital, Yangsan, Republic of Korea.
3 Department of Orthopaedic Surgery, BioMedical Research Institute, Pusan National University Hospital, Busan, Republic of Korea.
4 Department of Nuclear Medicine, Pusan National University Yangsan Hospital, Yangsan 50612, Republic of Korea.
5 BioMedical Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, Republic of Korea.
6 Department of Nuclear Medicine, College of Medicine, Pusan National University, Yangsan, Republic of Korea.