This study aims to evaluate the effectiveness of [18F]-DPA-714 PET imaging in detecting neuroimmune activity in patients with autoimmune encephalitis (AE). The primary objective is to compare [18F]-DPA-714 binding in AE patients to healthy controls.

Autoimmune encephalitis (AIE) constitutes a heterogeneous group of rare diseases affecting the central nervous system. They are distinguished by the presence of different antibody types and clinical manifestations. The diagnosis is inherently challenging due to the heterogeneity of symptoms, yet it is of paramount importance for the expeditious initiation of treatment. The current diagnostic criteria, established in 2016, define AIS as follows: possible, definite and seronegative. However, these criteria have limitations in terms of sensitivity and specificity. Furthermore, the diagnostic tools that are typically employed to detect inflammatory abnormalities in the central nervous system (brain MRI and analysis of CSF) are frequently inadequate in this condition. Positron emission tomography (PET) imaging targeting the 18-kDa translocator protein (TSPO) is emerging as a promising approach for the in vivo assessment of neuro-immune activity in EAI.

The objective of the proposed research project is to examine neuro-immune activity on PET imaging at the onset of EAI. The procedure involves a 60-minute dynamic PET scan immediately after [18F]-DPA-714 injection. Patients will undergo clinical evaluation, MRI, and lumbar puncture as part of their standard care. Follow-up will include analysis of PET images, comparison with healthy controls, and comparison between PET results and conventional biomarkers (MRI, CSF analysis).

Inclusion Criteria:

• Age 18-80 years;
• meeting clinical criteria for "possible" AE with identified antibodies;
• newly diagnosed with symptoms <6 months;
• no second-line immunosuppressive treatment;
• high or mixed TSPO binding affinity phenotype.

Exclusion Criteria:

• Pregnant women;
• contraindications to MRI;
• known allergic reaction to [18F]-DPA-714; legal protection measure;
• paraneoplastic syndrome following immune checkpoint inhibitor therapy.