Brain ¹⁸F-FDG PET for the diagnosis of autoimmune encephalitis: a systematic review and a meta-analysis

Objective: To consolidate current understanding of detection sensitivity of brain ¹⁸F-FDG PET scans in the diagnosis of autoimmune encephalitis and to define specific metabolic imaging patterns for the most frequently occurring autoantibodies.

Methods: A systematic and exhaustive search of data available in the literature was performed by querying the PubMed/MEDLINE and Cochrane databases for the search terms: ((PET) OR (positron emission tomography)) AND ((FDG) OR (fluorodeoxyglucose)) AND ((encephalitis) OR (brain inflammation)). Studies had to satisfy the following criteria: (i) include at least ten pediatric or adult patients suspected or diagnosed with autoimmune encephalitis according to the current recommendations, (ii) specifically present ¹⁸F-FDG PET and/or morphologic imaging findings. The diagnostic ¹⁸F-FDG PET detection sensitivity in autoimmune encephalitis was determined for all cases reported in this systematic review, according to a meta-analysis following the PRISMA method, and selected publication quality was assessed with the QUADAS-2 tool.

Results: The search strategy identified 626 articles including references from publications. The detection sensitivity of ¹⁸F-FDG PET was 87% (80-92%) based on 21 publications and 444 patients included in the meta-analysis. We also report specific brain ¹⁸F-FDG PET imaging patterns for the main encephalitis autoantibody subtypes.

Conclusion and relevance: Brain ¹⁸F-FDG PET has a high detection sensitivity and should be included in future diagnostic autoimmune encephalitis recommendations. Specific metabolic ¹⁸F-FDG PET patterns corresponding to the main autoimmune encephalitis autoantibody subtypes further enhance the value of this diagnostic.