Simultaneous ¹⁸F-FDG PET/MR metabolic and structural changes in visual snow syndrome and diagnostic use

Visual snow syndrome (VSS) is a recently recognized chronic neurologic condition characterized by the constant perceiving of tiny flickering dots throughout the entire visual field. Metabolic overactivity and grey matter volume increase in the lingual gyrus has been reported. We investigated this by ¹⁸F-FDG PET/MR in comparison to healthy controls. Aside from voxel-based characterization, the classification accuracy of volume-of-interest (VOI)-based multimodal assessment was evaluated, also in comparison with visual analysis.

Simultaneous ¹⁸F-FDG PET and MR imaging was performed in 7 patients with VSS (24.6 ± 5.7 years; 5 M/2F) and 15 age-matched healthy controls (CON) (28.0 ± 5.3 years; 8 M/7F). SPM12 and voxel-based morphometric analysis was performed. A VOI-based discriminant analysis was performed with relative ¹⁸F-FDG uptake, MR grey matter (GM) volumes and their combination. A visual analysis was done by two blinded experienced readers.

Relative increased hypermetabolism was found in VSS patients in the lingual gyrus and cuneus (p_FWE < 0.05, peak change + 24%), and hypometabolism in the mesiotemporal cortex (p_{height,uncorr} < 0.001, peak change - 14%). VSS patients also had increased GM volume in the limbic system and frontotemporal cortex bilaterally (p_FWE < 0.05), and in the left secondary and associative visual cortex and in the left lingual gyrus (p_{height,uncorr} < 0.001). Discriminant analysis resulted in 100% correct classification accuracy for ¹⁸F-FDG with lingual gyrus, cuneus and lateral occipital lobe (BA 17 and BA 18) as main discriminators. Unimodal MR- and combined ¹⁸F-FDG + MR classification resulted in an accuracy of 91% and 95%, respectively. Visual analysis of ¹⁸F-FDG was highly observer dependent.

Patients with VSS have highly significant structural and metabolic abnormalities in the visual and limbic system. VOI-based discriminant analysis of ¹⁸F-FDG PET allows reliable individual classification versus controls, whereas visual analysis of experienced observers was highly variable. Further investigation in larger series, also in comparison to VSS mimicking disorders such as migraine, is warranted.

Retrospectively registered at clinicaltrials.gov under NCT05569733 on Oct 5, 2022.