Purpose: Depression is common in Parkinson's disease (PD) and is correlated with the severity of motor deficits and quality of life. The present study aimed to investigate alterations in the structural brain network related to depression in Parkinson's disease (d-PD) and their correlations with structural impairments of white matter (WM).Materials and Methods: Data were acquired from the Parkinson Progression Markers Initiative (PPMI) database. A total of 84 de novo and drug-naïve PD patients were screened and classified into two groups according to the 15-item Geriatric Depression Scale (GDS-15): d-PD (n = 28) and nondepression in PD (nd-PD, n = 56). Additionally, 37 healthy controls (HC) were screened. All subjects underwent DTI and 3D-T1WI on a 3.0 T MR scanner. Individual structural brain networks were constructed and analyses were performed using graph theory and network-based statistics (NBS) at both global and local levels. Differences in global topological properties were explored among the three groups. The association models between node and edge changes and the GDS-15 were constructed to detect regions that were specifically correlated with d-PD. Tract-based spatial statistics (TBSS) was used to detect structural impairments of WM between the d-PD and nd-PD groups. The correlations between altered global topological properties and structural impairments were analyzed in the d-PD group.Results: The global efficiency and characteristic path length of the structural brain network were impaired in the d-PD group compared with those in the nd-PD and HC groups. Thirteen nodes and 1 subnetwork with 10 nodes and 12 edges specifically correlated with d-PD were detected. The left hippocampus, left parahippocampal, left lingual, left middle occipital, left inferior occipital, left fusiform, left middle temporal, and left inferior temporal regions were all involved in the results of node and edge analysis. No WM microstructural impairments were identified in the d-PD group.Conclusion: Our study suggests that the integration of the structural brain network is impaired with disrupted connectivity of limbic system and visual system in the de novo and drug-naïve d-PD patients.The topological properties assessing integration of the structural brain network can serve as a potential objective neuroimaging marker for early diagnosis of d-PD.

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Minimal hepatic encephalopathy (MHE), as an early stage of hepatic encephalopathy (HE), shows only mild attention deficit, visual motor dysfunction, cognitive control impairment and working memory network disorder, without any obvious neurologic manifestations (e.g., confusion, hepatic coma). As a transitional stage, 20%-80% of MHE cases develop from liver cirrhosis (1). Patients usually have weaker capabilities of handling an emergency situation and higher risk of accident (2). MHE is potentially reversible, because of the minor damage to the neurons (3).Previously, diffusion tensor imaging and magnetic resonance spectrum were used to get an insight into HE. These modalities found neuron swelling or interstitial edema and abnormal metabolism in related brain regions (4-8).Currently, blood oxygenation level dependent-functional magnetic resonance imaging (BOLD-fMRI), which has the ability to detect brain dysfunction, is a focus in the field of HE research. Some task-related fMRI studies found impairments in multiple cognitive and spatial memory functional regions of the brain (9, 10). Different from task-related fMRI, resting-state fMRI demonstrates spontaneous neuronal activity. Using resting-state fMRI, studies found decreased regional homogeneity in brain regions that are related to cognition and memory function, and the changes of regional homogeneity in the precuneus were closely related to the development of MHE (11,12). Functional connectivity was also used in HE studies, which revealed disturbed brain networks (13)(14)(15)(16)(17)(18).A different approach from regional homogeneity and functional connectivity, amplitude of low frequency fluctuation (ALFF) analysis, which detects the alternation of spontaneous brain activity by measuring the energy of low frequency oscillation, was first used by Zang et al. (19) METHODSA total of 14 MHE patients and 14 healthy controls were included in our study. Both ALFF and fALFF of functional magnetic resonance imaging were calculated for statistical analysis. RESULTSCompared with healthy controls, patients with MHE had significantly decreased ALFF in the bilateral medial prefrontal cortex (MPFC), left superior frontal gyrus, right precentral gyrus, left opercular part of inferior frontal gyrus, left gyrus rectus, bilateral precuneus, and the posterior lobe of right cerebellum; and they had significantly decreased fALFF in the bilateral MPFC, right middle frontal gyrus, right superior temporal gyrus, and the posterior lobe of left cerebellum. CONCLUSIONALFF and fALFF changes in many brain regions demonstrate abnormality of the spontaneous neuronal activity in MHE. Especially the impairment of right precuneus and left MPFC may play a critical role in manifestation of MHE. Changes of ALFF and fALFF in the precuneus and the MPFC can be used as a potential marker for MHE.

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