Objective: In this study, we focused on identifying the resting ¹⁸F-FDG PET brain imaging patterns in the limbic region and measuring the MRI volumes of the hippocampal subfields and limbic region in patients with functional tremor.

Background: Functional tremor is the most common functional movement disorder and advances in neuroimaging techniques have allowed for a greater understanding of neural-system dysfunction in functional neurological disorders.

Method: We studied 11 patients with functional tremor, 15 with essential tremor, and 15 with normal healthy controls. All participants underwent resting ¹⁸F-FDG PET brain imaging and structural MRI. Region-based analyses were confined to a priori regions of interest. The FDG peak mean uptake value within each limbic region was calculated and used in the statistical analyses. MRI volumetric segmentation was performed with FreeSurfer software. Comparison was made between the functional tremor group, essential tremor group, and healthy controls, using multivariate analysis of variance. Age, sex, and tremor duration were included as covariates. The statistical threshold was set at p<0.05 after the false discovery rate (FDR) method correction for multiple comparisons.

Results: Although no validated psychometric assessments were employed, all functional tremor patients indicated significant stress-related concerns during clinical interviews, including sexual assault. Rest FDG-PET imaging showed increased glucose metabolism in the left anterior hippocampus in the functional tremor group compared to the healthy control group. The MRI findings showed reduced volume in the left hippocampus in CA3, CA4, and dentate gyrus subfields in the functional tremor group compared to the healthy control group.

Conclusion: This is the first study describing abnormally increased brain glucose metabolism in the anterior hippocampus and the hippocampal subfield in functional neurological disorders. The increased FDG uptake may be related to mind-wandering phenomena and may account for the hypervigilance and hyperarousal state in patients with functional neurological disorders, while the hippocampal subfield structural abnormalities may be associated with the previous significant stress situations. Further studies are needed to confirm this finding combined with validated psychometric measurements.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/increased-resting-anterior-hippocampus-metabolism-and-hippocampus-subfields-structural-abnormalities-in-functional-tremor-patients-fdg-pet-study-and-volumetric-mri-study/