F-FDG PET/CT Reveals Characteristic Prefrontal-Posterior Cingulate Hypometabolism in anti-AMPAR Encephalitis to Understand Cerebral Function: Insights From an Eight-Patient Cohort.

[PURPOSE] Anti-AMPAR encephalitis is a rare antibody-mediated disorder, and its clinicoradiological profile is incompletely defined. We aimed to characterize the clinical presentation and cerebral metabolic patterns of Chinese adults with anti-AMPAR encephalitis using F-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 F-FDG PET/CT findings (Discovery Elite, GE Healthcare), 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 F-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 cingulate hypometabolism on F-FDG PET/CT. In some instances, hypermetabolism was observed in the basal ganglia or temporal lobes, possibly reflecting the local blood flow.