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

Abstract

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.

Keywords: autoimmune encephalitis; diagnosis; gamma-aminobutyric-acid B receptor; outcome; positron emission tomography.

FIGURE 1

Comparisons between MRI and ¹⁸F‐FDG‐PET in patients with anti‐GABAB receptor encephalitis. (A) Neuroimaging testing plays an essential role in the diagnosis of anti‐GABAB receptor encephalitis. The sensitivity of ¹⁸F‐FDG‐PET is higher than that of MRI; (B) representative images in one patient with anti‐GABAB receptor encephalitis (patient #3): ¹⁸F‐FDG‐PET is positive (c and d) even if MRI is negative (a and b); (C) brain hypermetabolism limited to MTL structures in same representative case based on semi‐quantitative statistical parametric mapping method. Abbreviations: ¹⁸F‐FDG‐PET, ¹⁸F‐fluorodeoxy‐glucose positron emission tomography; GABAB, gamma‐aminobutyric‐acid B receptor; MTL, medial temporal lobe; MRI, magnetic resonance imaging

FIGURE 2

The results of ¹⁸F‐FDG‐PET pattern in anti‐GABAB receptor encephalitis. (A) Representative images of abnormal metabolism in individual patient (patient #13). Hypermetabolism pattern: MTL; hypometabolism pattern: frontal and parietal lobe (FWE corrected, p < 0.05). (B) Groupwise analysis confirms MTL hypermetabolism in association with relative hypometabolism in frontal and parietal lobe, extending to cingulate gyrus, is a general metabolic pattern in subjects with anti‐GABAB receptor encephalitis (FDR corrected, p < 0.05). Significant hyper‐ and hypometabolism is color coded as shown in legend. Renders created using Brain Net Viewer (Xia et al., 2013) (https://www.nitrc.org/projects/bnv/). Abbreviations: ¹⁸F‐FDG‐PET, ¹⁸F‐fluorodeoxy‐glucose positron emission tomography; FDR, false discovery rate; FEW, familywise error; GABAB, gamma‐aminobutyric‐acid B receptor; Hyper, hypermetabolism; Hypo, hypometabolism; MTL, medial temporal lobe

FIGURE 3

Correlation analysis between long‐term outcome and ¹⁸F‐FDG‐PET based on statistical parametric mapping method in patients with anti‐GABAB receptor encephalitis. Compared to patients with good outcome, patients with poor outcome demonstrated relatively increased metabolism in the MTL (uncorrected, p < 0.001). Abbreviations: ¹⁸F‐FDG‐PET, ¹⁸F‐fluorodeoxy‐glucose positron emission tomography; GABAB, gamma‐aminobutyric‐acid B receptor; MTL, medial temporal lobe