Longitudinal Characterization of Vascular Inflammation and Disease Activity in Takayasu Arteritis and Giant Cell Arteritis: A Single-Center Prospective Study

Objective: To examine and compare disease activity over time in giant cell arteritis (GCA) and Takayasu arteritis (TAK) using multimodal assessment combining clinical, laboratory, and imaging-based testing. Methods: Patients with GCA or TAK were enrolled into a single-center prospective, observational cohort at any point in the disease course. Patients underwent standardized assessment, including ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) at enrollment and follow-up visits. Each FDG-PET finding was subjectively interpreted as active or inactive vasculitis. Global arterial FDG uptake was quantified by the PET Vascular Activity Score (PETVAS). Patients were stratified by disease duration at enrollment (0–2 years; 2–5 years; >5 years). Fisher exact and Mann-Whitney U tests, Spearman's correlation, and linear regression were used for statistical analyses. Results: A total of 126 patients with large vessel vasculitis (GCA = 50; TAK = 76) were evaluated across 319 visits. Clinical disease activity was present in 33% of patients in the second to fifth year of disease and in 24% of patients evaluated >5 years after diagnosis. Active vasculitis by PET was observed in 66% of patients in years 2 to 5 after diagnosis and in 50% of patients enrolled >5 years into disease. PETVASs were consistently higher in GCA than TAK in the early and later phases of disease and significantly decreased over time in GCA but not TAK. Correlations between clinical, laboratory, and imaging findings were complex and varied with disease duration. Conclusion: Disease activity in GCA and TAK is common throughout the disease course. Patterns of vascular PET activity at diagnosis and later in disease differ between GCA and TAK.