Regional Metabolic Abnormalities in Autoimmune Encephalitis

Purpose Autoimmune encephalitis (AIE) is a group of conditions that are insufficiently understood and difficult to diagnose. Several publications indicate that FDG PET has superior sensitivity compared with MRI. This study aimed to perform a systematic review of publications to assess the characteristics and frequency of brain FDG PET compared with MRI findings at the individual level in AIE, including case reports and case series. The resulting meta-analysis is complementary to previous publications with large or medium-sized cohorts. Patients and Methods The review was performed using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and aimed to identify all studies with at least 1 case of AIE in which brain FDG PET was performed. Results from MRI and FDG PET were extracted on a patient-by-patient basis. Results The literature search yielded 1303 results, of which 234 studies were included, containing 498 cases. Abnormal FDG PET findings are reported in 93% compared with 55% with MRI. The affected brain regions, rates of unilateral versus bilateral findings, and hypermetabolism versus hypometabolism are descriptively presented in tables categorized according to the associated antibody. Conclusions FDG PET detected abnormalities more frequently than MRI, particularly in cases with anti-NMDAR and anti-GABA-B antibodies. Findings include a high prevalence of hypermetabolism in the medial temporal lobes, but also a high prevalence of parietal and occipital hypometabolism. Results differed depending on the associated antibody. Overall, the findings strengthen the importance of FDG PET in patients with suspected AIE, and the antibody-related patterns of regional metabolic abnormalities indicate a high potential for further development as a diagnostic and prognostic tool.