Prediction of Response to Tumor Necrosis Value-α Blocker Is Suggested by ¹⁸F-NaF SUV_max But Not by Quantitative Pharmacokinetic Analysis in Patients With Ankylosing Spondylitis.

Abstract

<b>OBJECTIVE.</b> We aimed to evaluate the pharmacokinetics and maximum standardized uptake value (SUV_max) of ¹⁸F-NaF PET/CT for assessment of disease activity and prediction of response in patients with ankylosing spondylitis (AS). <b>MATERIALS AND METHODS.</b> 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 SUV_max of the SIJs and SUV_max 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. <b>RESULTS.</b> 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 SUV_max of the spine had a significant positive correlation with BASDAI score at PET/CT (<i>r</i> = 0.38, <i>p</i> = 0.048). The BASDAI score at PET/CT (odds ratio [OR], 35.32; 95% CI, 2.09-57.84; <i>p</i> = 0.014) and SUV_max of the spine (OR, 14.69; 95% CI, 0.79-27.27; <i>p</i> = 0.027) were significantly associated with BASDAI 50 response prediction. <b>CONCLUSION.</b> The results of our study suggest that the SUV_max 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.