195. Use of 18F-fluorodeoxyglucose Positron Emission Tomography to Standardize Clinical Trial Recruitment in Takayasu's Arteritis

Background: Disease activity assessment can be challenging in Takayasu’s arteritis (TAK), which can lead to difficulty in determining eligibility for enrollment into randomized clinical trials (RCTs). FDG-PET can complement clinical assessment of disease activity. The study objective was to assess whether data from FDG-PET should be incorporated into eligibility criteria for clinical trials in TAK. Methods: The study was conducted in two parts. Part One was an international online survey among physicians with experience managing TAK to determine whether FDG-PET data influences decisions about enrollment in trials. Participants were asked background questions, including personal experience with use of PET. Clinical vignettes of commonly encountered clinical scenarios were presented, based on actual cases derived from a prospective, observational cohort. In section A of each vignette, clinical symptoms, examination findings, acute phase reactant (APR) levels, and angiographic data were presented. Participants were asked if there was sufficient evidence of active vasculitis to enroll the patient into an RCT studying a new treatment agent (yes or no) and to rate level of confidence about their assessment (scale of 0-100). In section B, detailed information from the same patient’s PET scan was presented and participants were again asked whether they would enroll the patient into an RCT (yes or no) and level of confidence about their assessment. Part Two used patient-level data from an observational cohort study in TAK to assess agreement regarding decisions about enrollment into trials, based on clinical assessment with and without incorporation of FDG-PET data. Generalized linear mixed models, adjusting for correlated data, were used to evaluate associations between PET activity, APR levels, and enrollment decisions. Results: In Part One 68 physicians responded to the survey. Most physicians had used FDG-PET to diagnose TAK (82%) or monitor disease activity over time (66%). In Section A of the vignettes, greater variability in trial enrollment decision was observed in cases of constitutional symptoms alone (e.g. fatigue) and elevated APR levels (Cases 4-6) (Table 1). In Section B, level of confidence improved when PET findings aligned with clinical assessment from Part A (Case 1,3,8). In cases where PET findings did not align with clinical assessment in part A (e.g. absent clinical symptoms with active PET scan, “subclinical inflammation”), the degree of variability about whether to enroll/not enroll increased in Section B and level of confidence worsened (Case 2, 7). In cases with the highest variability about enrollment in Section A (Cases 4-6), PET activity drove the decision of whether to enroll in Section B and level of confidence improved (Table 1). In multivariable models, FDG-PET findings were 1.29 times more strongly associated with enrollment decisions compared to levels of APRs. In Part Two, incorporation of FDG-PET data significantly improved agreement about enrollment decisions between raters, (IRR=0.68 [95%CI (0.67-0.69)] to IRR=0.88 [95%CI 0.87-0.89]; p