Distinguishing autoimmune encephalitis from its mimics using brain [¹⁸F]-FDG PET: real-world study

Area of Science:

• Neuroimaging
• Nuclear Medicine
• Neurology

Background:

• Diagnosing autoimmune encephalitis (AE) is challenging due to varied symptoms, seronegativity, and low MRI sensitivity.
• Brain [¹⁸F]-FDG PET/CT is evaluated as a diagnostic tool for suspected AE in a real-world clinical setting.

Purpose of the Study:

• To assess the diagnostic performance of brain [¹⁸F]-FDG PET/CT in patients with suspected autoimmune encephalitis.
• To identify characteristic metabolic patterns of AE using [¹⁸F]-FDG PET/CT and differentiate it from mimics.

Main Methods:

• Retrospective analysis of 141 patients undergoing [¹⁸F]-FDG PET/CT for suspected AE.
• Final diagnoses established using international criteria and expert consensus.
• PET findings analyzed visually and quantitatively, compared with healthy controls, and stratified by age.

Main Results:

• Autoimmune encephalitis (AE) cases (33%) exhibited cortical hypometabolism and mesiotemporal lobe (MTL), basal ganglia, cerebellum, midbrain, and insula hypermetabolism.
• [¹⁸F]-FDG PET/CT effectively discriminated AE from differential diagnoses (AUC 0.82-0.83), with MTL hypermetabolism being a key feature.
• Diagnostic accuracy was highest in patients under 40, with positive/negative predictive values of 82%/81% for visual PET analysis.

Conclusions:

• Brain [¹⁸F]-FDG PET/CT reveals a characteristic metabolic signature for AE, aiding in its differentiation from other neurological conditions.
• The study supports [¹⁸F]-FDG PET/CT as a valuable complementary diagnostic biomarker for AE, particularly in younger patient populations.