Imaging features of 18F-FDG PET/CT in patients with autoimmune encephalitis

Objective To study the imaging features of 18F-fluorodeoxyglucose(FDG) PET/CT in patients with autoimmune encephalitis (AE) and evaluate the value of PET/CT on early diagnosis of AE. Methods Sixteen patients with AE (11 males, 5 females, age: 11-68 years) between March 2012 and December 2017 were included. Patients had positive antibodies in cerebrospinal fluid or (and) serum without immunity therapy. The imaging (18F-FDG PET/CT, MRI) and clinical data were analyzed. Results Nine patients suffered from anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis and other 7 patients had limbic encephalitis (LE), which including 2 cases of anti-leucine-rich glioma inactivated 1(LGI1) encephalitis, 3 cases of anti-γ-aminobutyric acid-B receptor(GABABR) encephalitis, 1 case of anti-Hu encephalitis and 1 case of anti-Yo encephalitis. Fifteen patients showed scattered hypermetabolism or hypometabolism in the brain on PET/CT imaging, and the positive rate was 15/16. Among those patients with anti-NMDAR encephalitis, hypermetabolism in frontotemporal parietal lobes and hypometabolism in occipital lobe were shown; hypermetabolism in limbic systems including temporal lobe and hippocampus were shown in LE. No abnormal CT density was found at the same phase. Slightly higher signals on T2, fluid-attenuated inversion recovery (FLAIR) and diffusion weighted imaging (DWI) were detected in some patients, and the positive rate was 7/16. Conclusions Patients with AE of different types have different characteristics on 18F-FDG PET/CT. 18F-FDG PET/CT has high positive rate for early diagnosis of AE. Key words: Encephalitis; Autoimmune diseases; Positron-emission tomography; Tomography, X-ray computed; Deoxyglucose