The goal of this retrospective observational study is to compare brain fluorodeoxyglucose-positron emission tomography (FDG-PET) of patients with autoimmune encephalitis, normal controls and patients with Alzheimer's disease (AD). The main question it aims to answer is: •is there a specific pattern of brain metabolism in patients with autoimmune encephalitis Participants data and images will be retrospectively collected from hospital records, and FDG-PET images will be analyzed by means of statistical parametric mapping (SPM). Controls will be selected from validated public databases.