18 F‐fluorodeoxy‐glucose positron emission tomography pattern and prognostic predictors in patients with anti‐GABAB receptor encephalitis

Aims To identify the metabolic pattern and prognostic predictors in anti‐gamma‐aminobutyric‐acid B (GABAB) receptor encephalitis using 18F‐fluorodeoxy‐glucose positron emission tomography (18F‐FDG‐PET). Methods Twenty‐one patients diagnosed anti‐GABAB receptor encephalitis who underwent 18F‐FDG‐PET at first hospitalization were retrospectively reviewed. 18F‐FDG‐PET images were analyzed in comparison with controls. Further group comparisons of 18F‐FDG‐PET data were carried out between prognostic subgroups. Results 18F‐FDG‐PET was abnormal in 81% patients with anti‐GABAB receptor encephalitis and was more sensitive than MRI (81% vs. 42.9%, p = 0.025). Alter limbic lobe glucose metabolism (mostly hypermetabolism) was observed in 14 patients (66.7%), of whom 10 (10/14, 71.4%) demonstrated hypermetabolism in the medial temporal lobe (MTL). Group analysis also confirmed MTL hypermetabolism in association with relative frontal and parietal hypometabolism was a general metabolic pattern. After a median follow‐up of 33 months, the group comparisons revealed that patients with poor outcome demonstrated increased metabolism in the MTL compared to those with good outcome. Conclusion 18F‐FDG‐PET may be more sensitive than MRI in the early diagnosis of anti‐GABAB receptor encephalitis. MTL hypermetabolism was associated with relative frontal or parietal hypometabolism and may serve as a prognostic biomarker in anti‐GABAB receptor encephalitis.
First, we revealed pronounced MTL hypermetabolism detected by semi‐quantitative brain 18F‐FDG‐PET in patients with anti‐GABAB receptor encephalitis compared to controls, and 18F‐FDG‐PET should be considered when patients with normal MRI in suspected anti‐GABAB receptor encephalitis; second, MTL hypermetabolism may be a sensitive diagnostic and prognostic biomarker for anti‐GABAB receptor encephalitis.