[18F]-FDG-PET/CT detects subclinical optic nerve inflammation in giant cell arteritis.

Vision loss is a feared complication in giant cell arteritis (GCA). However, imaging data characterizing intraorbital inflammation and its potential predictive value for ischemic ocular complications remain limited. Such information might be helpful in clinical phenotyping and risk stratification of patients with GCA. This is a retrospective cohort study of patients with GCA, who received at least two [18F]-FDG-PET/CTs. Quantitative assessment included measurement of SUVmax, SUVmean, and the target-to-background ratio (TBR) of both optic nerves (ONs) in the canalicular segment, serving as a surrogate for [18F]-FDG uptake. A total of 18 patients were included; only 1 had visual symptoms. [18F]-FDG uptake of the ONs was higher in active GCA than in a control cohort [i.e., patients with a primary diagnosis of bronchial carcinoma; median TBR 8.0 (interquartile range 5.2-10.0) vs. 1.8 (1.6-2.5), respectively; p < 0.0001]. Under immunosuppressive therapy, the [18F]-FDG uptake of the ONs declined [median TBR of inactive GCA was 5.5 (4.3-7.2), p = 0.0009 vs. active GCA]. A TBR of 7.5 distinguishes between active and inactive GCA with a sensitivity of 86.7% and a specificity of 61.1% [area under the curve (AUC) 0.743, 95% confidence interval (CI) 0.574-0.912, p = 0.0179]. An unexpected high uptake of [18F]-FDG, corresponding to inflammation of the ONs, could be detected in patients with GCA, most of whom exhibited no visual symptoms. Under immunosuppressive therapy, [18F]-FDG uptake declined, indicating treatment response. These findings suggest that subclinical ON inflammation in GCA may be more prevalent than previously recognized.