PET/CT reveals characteristic prefrontal- Posterior cingulate hypometabolism in anti- AMPAR encephalitis

We aimed to characterize the clinical presentation and cerebral metabolic patterns of Chinese adults with anti- AMPAR encephalitis using 18F- FDG PET/CT. Methods: From August 2016 to August 2022, we retrospectively identified patients from two neurology centers who were positive for anti- AMPAR antibodies in serum and/or cerebrospinal fluid. Demographic data, presenting symptoms, MRI and 18F- FDG PET/CT findings, treatment regimens, and outcomes were extracted and analyzed. Results: Eight patients (four women) were included; median age was 53 years (range 37–63). Anti- AMPA2R antibodies were detected in seven cases and anti- AMPA1R antibodies in one. Limbic manifestations dominated, particularly cognitive decline and abnormal behavior; severe disease necessitated intensive care support in one patient, who nonetheless achieved a good outcome. Malignancy was documented in three individuals (lung carcinoma, hepatocellular carcinoma, and thymoma), and three harbored additional neural autoantibodies. MRI was abnormal in five patients (62.5%). All five subjects who underwent 18F- FDG PET/CT displayed prefrontal hypometabolism; three also showed posterior cingulate hypometabolism. Focal hypermetabolism was observed in the right temporal lobe (one case) and in the left thalamus (one case). Conclusion: Anti- AMPAR encephalitis usually presents as limbic encephalitis and is marked by prefrontal and posterior cingu late hypometabolism on 18F- FDG PET/CT. In some instances, hypermetabolism was observed in the basal ganglia or temporal lobes, possibly reflecting the local blood flow.

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