Background/Purpose:   FDG-PET can be used to detect vascular inflammation in large vessel vasculitis (LVV). The study objective was to determine if therapies currently used to treat LVV impact vascular FDG uptake.

Methods:   Patients with giant cell arteritis (GCA) or Takayasu’s arteritis (TAK) were recruited into a prospective, observational cohort of LVV. All patients underwent FDG-PET/CT at 6-month intervals (256 matrix, 3mm slice, 2 hour uptake time). Change in cumulative glucocorticoid (GC) dose between interval visits was calculated. Treatment status between interval visits was categorized as increased, decreased, or unchanged. Change in treatment was defined as change in average daily dose of prednisone over past 7 days by ≥ 5 mg, addition of a new DMARD or biologic agent or a 50% change from the baseline dose. Standardized uptake values (SUVs) were measured in 3 regions: 1) ascending aorta and arch; 2) descending aorta; and 3) liver. Vascular FDG uptake was quantified as a target to background ratio (TBR) standardized to the liver (TBR = SUV_max Aorta Region / SUV_mean Liver). Change in TBR in each region of the aorta was calculated between interval study visits. Kruskal-Wallis test was performed to compare change in TBR across treatment status categories. Spearman correlation between change in TBR, change in cumulative GC dose, and change in methotrexate (MTX) dose was calculated. Linear regression was performed to evaluate relationship between change in MTX and GC dose with change in TBR.

Results:   FDG-PET/CT was performed in 20 patients with LVV (GCA=14; TAK=6) over 49 study visits. 15 patients were treated with GCs, 10 patients were treated with MTX, and 8 patients received another DMARD or biologic during the study. Increased therapy was recorded over 11 visit intervals, decreased treatment was noted in 5 visit intervals, and there was no change in therapy for 11 visit intervals. There was a simultaneous decrease in the GC dose with increase of DMARD over 2 treatment intervals, which were excluded from further analysis. Change in TBR of the descending aorta significantly differed among the 3 treatment categories (p=0.01). Post hoc analysis showed significant reduction in TBR in the group with increased treatment versus the unchanged treatment group. A similar trend was observed in the TBR of the ascending aorta and arch among the 3 treatment groups but differences between groups were less pronounced and did not reach statistical significance (p=0.08). There was no change in the SUV_mean of the liver with change in treatment. Change in TBR of the descending aorta was inversely correlated with change in cumulative dosage of GC (r=-0.40, p=0.03) and with change in daily dose of methotrexate (r=-0.67; p=0.01). In multivariable regression, change in GC dose and change in methotrexate dose were independently associated with a change in TBR of the descending aorta (p<0.05).

Conclusion:   Therapies commonly used to treat LVV, including glucocorticoids and methotrexate, can reduce FDG vascular uptake in the aorta. Interval change in PET activity is more pronounced in the descending aorta compared to the ascending aorta and arch. FDG-PET might be useful to monitor vascular disease activity as an outcome measure in clinical trials of LVV.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/vascular-inflammation-assessed-by-18f-fludeoxyglucose-positron-emission-tomography-fdg-pet-is-modified-by-treatment-in-patients-with-large-vessel-vasculitis/