Follow-Up 18F-Fluorodeoxyglucose Positron Emission Tomography in Treated Patients With Giant Cell Arteritis: A Systematic Review and Metaanalysis

Objective Imaging biomarkers for disease activity are urgently needed in giant cell arteritis (GCA). Whether 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) can be used to monitor disease activity in patients with large-vessel GCA (LV-GCA) is still unclear. This study aimed to determine how often large-vessel inflammation improves or becomes radiographically quiescent on follow-up PET in patients with LV-GCA who show clinical improvement with treatment. Methods Medical Literature Analysis and Retrieval System Online (MEDLINE), Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Scopus, and the Cochrane Library were searched from inception through February 29, 2024. Studies describing patients with active LV-GCA on baseline PET who underwent follow-up PET and clinical assessment of disease activity after escalation of immunosuppressive therapy were included. Metaanalysis of the pooled sensitivities of improved PET for clinical improvement and normalized PET for clinical remission in treated patients with GCA 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 in 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 were 1.00 (95% CI 0.99-1.00) and 0.78 (95% CI 0.50-0.97), respectively. Conclusion Follow-up PET findings improved in most patients (95%) with LV-GCA who showed clinical improvement with treatment, but large-vessel vasculitis became radiographically quiescent in only 53% of patients. Better responses were observed in those receiving TCZ. (PROSPERO ID: CRD42020219141)