Impact of Confirmed Autoimmune Encephalitis on Brain Glucose Metabolism

Inclusion Criteria: * Age ≥ 18 years old * Newly diagnosed autoimmune encephalitis based on at least 1 of the 3 following criteria : 1. " Definite limbic autoimmune encephalitis " according to 2016 Graus et al. criteria 2. " Possible autoimmune encephalitis " according to 2016 Graus et al. criteria AND typical autoantibody detected in serum or CSF 3. " Probable or certain paraneoplastic neurological syndrome " according to Graus et al. 2021 criteria (excluding peripheral neurological syndromes) * Less than 6 months since first neurological symptoms imputable to autoimmune encephalitis * Affiliated or entitled to a social security system (except AME) * Obtaining free, written and informed consent (patient or legal representative or the close relative) Exclusion criteria * History of brain tumor, head trauma, infarction or cerebral hematoma likely to result in altered cerebral carbohydrate metabolism on PET * Patients who hae been on immunotherapy (corticosteroid bolus, IVIg, plasma exchange, endoxan, rituximab or other immunotherapy) fr more than 10 days * Pregnant or breast-feeding woman * Ventilated intubated patient * Absolute contraindication to MRI (Pacemaker, cochlear implant, etc.) * Presence of cognitive disorders incompatible with goog cooperation with the PET scan * Algic or agitated patient unable to remain immobile in supine position for 30 minutes * Deprived of liberty or under a protective measure (guardianship or curatorship) * Patient taking part in other interventional research involving radiopharmaceutical injections