Establishing imaging patterns on FDG PET/CT for specific antibody sub-types ofAutoimmune Encephalitis

Objectives: To establish specific imaging patterns on FDG PET/CT in different antibody sub-types of autoimmune encephalitis.

Methods: A total of 35 serologically proven cases of autoimmune encephalitis that underwent F-18 Fluoro-deoxy glucose (FDG) PET/CT scan were included. The patterns of FDG uptake in different antibody subtypes were recorded and comparison with normalized data was attempted. The areas of hypo/hyper metabolism that were two standard deviations from the mean were considered as abnormal. The patients were also analyzed based on the Z score surface maps of the 3D stereotactic surface projections (SSP) image and regional Z scores were evaluated. Post treatment follow-up scans were also acquired.

Results: All patients had an abnormal pattern of F-18 FDG uptake, both on visual inspection and semiquantitative analysis. Voltage gated potassium channel (VGKC) complex receptor antibody encephalitis patients were found to have typical areas of hypermetabolism in bilateral medial temporal regions and bilateral basal ganglia with relative global hypometabolism in rest of the cortical and subcortical structures. The subjects with N-methyl-D-aspartate-receptor antibody (NMDAR-Ab) encephalitis showed variable degrees of focal hypermetabolism in bilateral fronto-temporal regions, basal ganglia, thalami and cerebellar hemispheres with inhomogenous parieto-occipital hypometabolism. The post-treatment FDG PET/CT scans showed reversal to normal metabolism in the corresponding areas.

Conclusions: FDG PET/CT scan may serve useful as a non-invasive diagnostic modality in the early diagnosis and management of patients with clinical suspicion of autoimmune encephalitis.