(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 (18)F‐fluorodeoxy‐glucose positron emission tomography ((18)F‐FDG‐PET). METHODS: Twenty‐one patients diagnosed anti‐GABAB receptor encephalitis who underwent (18)F‐FDG‐PET at first hospitalization were retrospectively reviewed. (18)F‐FDG‐PET images were analyzed in comparison with controls. Further group comparisons of (18)F‐FDG‐PET data were carried out between prognostic subgroups. RESULTS: (18)F‐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: (18)F‐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.