Background/Purpose:

Disease activity in large vessel vasculitis (LVV) is traditionally assessed by clinical and serological (ESR, CRP) parameters. Imaging assessment, including FDG-PET, may also be useful to monitor LVV. The study objective was to determine if currently available therapies for LVV impact disease activity as assessed by clinical, serologic, and imaging-based parameters.

Methods:

Patients with giant cell arteritis (GCA) or Takayasu’s arteritis (TAK) were recruited into a prospective, observational cohort. All subjects in this study underwent ≥2 FDG-PET/CT scans at 6-month intervals. Serologic assessment (ESR, CRP), clinical assessment [physician global assessment (PGA)] and imaging assessment (PETVAS) was determined at each visit. PETVAS is a global summary score of arterial FDG uptake assessed qualitatively relative to liver activity in 9 vascular beds with higher scores indicating more vascular inflammation. Clinical and imaging assessments were performed blinded to each other. Treatment status between visits was categorized as increased, decreased, or unchanged. Treatment change was defined as change in daily prednisone by ≥5mg or addition/50% dose change of a DMARD or biologic therapy. Paired Wilcoxon test was used to compare changes in PETVAS, ESR, CRP and PGA with change in overall therapy and with addition/increase in specific medications.

Results:

FDG-PET/CT was performed in 33 patients with LVV (GCA=21; TAK=12) over 98 visits. Interval treatment changes involved glucocorticoids (n=32), methotrexate (n=13), tocilizumab (n=7), TNF inhibitors (n=7), or another DMARD/ biologic (n=6). Increased, decreased, or unchanged therapy was recorded over 27, 13, and 23 visit intervals respectively. There was simultaneous glucocorticoid reduction with DMARD increase over 2 intervals, which were excluded from analysis. In the increased treatment group, a significant reduction in PETVAS score (p<0.01), inflammatory markers (p<0.01) and PGA (p=0.01) was noted. In the decreased treatment group, PETVAS scores increased (p=0.05) but there was no change in ESR (p=0.3), CRP(p=0.2), or PGA (p=0.28). In the unchanged treatment group, PETVAS (p=0.88), ESR (p=0.8), CRP (p=0.6) and PGA (p=0.48) remained unchanged. In terms of specific therapies, addition of tocilizumab, resulted in significant reduction in PETVAS (p=0.01), acute phase reactants (p=0.01) and PGA (p=0.03), whereas TNF inhibitors and methotrexate addition/dose increase had variable effects on clinical, serological, and imaging parameters.

Conclusion:

Similar to clinical and serologic assessment, vascular inflammation assessed by FDG-PET improves with increased treatment and is stable without change in therapy. Unlike clinical and serological assessment, which did not change with reduction in treatment over a 6 month interval, vascular inflammation assessed by FDG-PET worsens with decreased therapy. Specific medications may affect vascular FDG uptake differently. These findings suggest that FDG-PET is useful to monitor treatment response and may be a more sensitive biomarker to detect disease recurrence in the setting of treatment reduction compared to clinical and serologic assessment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/assessment-of-treatment-response-by-18f-fludeoxyglucose-positron-emission-tomography-fdg-pet-in-patients-with-large-vessel-vasculitis-lvv/