How Often Does Follow up 18F-FDG PET Improve in Treated Patients with Giant Cell Arteritis: a Systematic Review and Meta-Analysis

Objective Imaging biomarkers for disease activity are urgently needed in giant cell arteritis (GCA). Whether 18F-fluorodeoxyglucose positron emission tomography (PET) can be used to follow disease activity in those with large vessel vasculitis (LV-GCA) is still unclear. We aimed to determine how often large vessel inflammation improves or becomes radiographically-quiescent on follow up PET in patients with LV-GCA who clinically improve on treatment. Methods MEDLINE, EMBASE, CINAHL, Scopus, and Cochrane Library were searched from inception through February 29, 2024. Studies describing patients with active LV-GCA on baseline PET, with a follow up PET scan repeated after escalating immunosuppression, and an assessment of clinical disease activity were included. Meta-analysis of the pooled sensitivity of 1) improved PET for clinical improvement and, 2) normalized PET for clinical remission in treated GCA patients was performed, with subgroup analysis of tocilizumab (TCZ)-treated patients. Results Of 3131 unique references, 25 studies were included. The pooled sensitivity of improved vascular FDG uptake on follow up PET for clinical improvement of GCA was 0.95 (95% CI 0.82-1.00), and the pooled sensitivity of normalized vascular FDG uptake on follow up PET for clinical remission was 0.53 (95% CI 0.34-0.72). In TCZ-treated patients, the pooled sensitivity of improvement and normalization of follow up PET was 1.00 (95% CI 0.99-1.00) and 0.78 (95% CI 0.50-0.97), respectively. Conclusion Follow up PET images improved in most (95%) patients with LV-GCA who clinically improved on treatment but LVV became radiographically quiescent in only 53%. Better responses were seen in those receiving TCZ.