Use of 18F-fluorodeoxyglucose Positron Emission Tomography to Monitor Tocilizumab Effect on Vascular Inflammation in Giant Cell Arteritis

Kaitlin A. Quinn; Himanshu Dashora; Elaine Novakovich; Mark A. Ahlman; Peter C. Grayson

Disclosures

Rheumatology. 2021;60(9):4384-4389. 

In This Article

Methods

Study Population and Assessment

Complete details about the study population are included in Supplementary Data S1, available at Rheumatology online. Briefly, patients with GCA were recruited from across North America into an ongoing prospective, observational cohort study at the National Institutes of Health (NIH) in Bethesda, MD (ClinicalTrials.gov, NCT02257866). All patients fulfilled modified 1990 ACR Classification Criteria for GCA.[10,11] To determine vascular response to tocilizumab, PET scan findings from the study visit immediately prior to the initiation of tocilizumab (baseline visit) were compared with imaging findings from all available subsequent follow-up visits, performed at ~6-month intervals. For patients who discontinued tocilizumab at any point during the study, FDG-PET imaging was also compared before and after discontinuation of tocilizumab.

Clinical Assessment and Management

At each visit, patients underwent clinical, laboratory and imaging assessments within a 24-h time period at the NIH Clinical Center. Clinical and imaging assessments were performed blinded to each other. Definitions of disease activity are included in Supplementary Data S1, available at Rheumatology online.

FDG-PET Imaging Assessment

One nuclear medicine physician (M.A.A.) with >10 years clinical FDG-PET experience interpreted all of the PET studies, blinded to all clinical data. Each study was interpreted as active or inactive vasculitis based on overall subjective assessment by the reader with excellent reliability as previously reported.[12–14] Qualitative assessment of FDG uptake relative to liver uptake by visual assessment was assessed in nine arterial territories. A summary score, PET vascular activity score (PETVAS), was calculated (scale 0–27), with higher scores indicating a greater global burden of vascular inflammation[14] (see Supplementary Data S1, available at Rheumatology online, for additional details and imaging protocol).

Statistical Analysis

The Wilcoxon signed rank test was used to compare change in PETVAS between two time points. Linear regression with P-value for linear trend was calculated to determine change in PETVAS over multiple timepoints. To determine whether the effect of tocilizumab on vascular inflammation was independent of glucocorticoid use, change in PETVAS was studied in a subset of patients treated with tocilizumab who were taking 10 mg daily prednisone or less at both imaging timepoints. The association between cumulative glucocorticoid dose and change in PETVAS was also assessed using Spearman's rank-order correlation.

Ethics and Informed Consent

All patients provided written informed consent. This study was approved by the National Institute of Arthritis and Musculoskeletal and Skin Diseases institutional review board (NIAMS IRB Protocol: 14-AR-0200).

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