Impaired Frontolimbic Connectivity and Depressive Symptoms in Patients with Alzheimer's Disease

The mediating effect of the amygdala-frontal circuit on the association between depressive symptoms and cognitive function in Alzheimer's disease

Depressive symptoms occur commonly in Alzheimer's disease (AD). Although abnormalities in the amygdala-frontal circuit have been linked to emotional dysregulation and cognitive impairment, the neurological basis underlying these associations in AD patients with depressive symptoms (ADD) is unclear. We aimed to investigate the relationship between the amygdala-frontal circuit and depressive symptoms and cognitive function in ADD. We recruited 60 ADD, 60 AD patients without depressive symptoms (ADND), and 60 healthy controls (HC). Functional connectivity (FC) maps of the bilateral amygdala were compared. Fractional anisotropy (FA) of the amygdala-frontal circuit connected by the uncinate fasciculus (UF) was calculated using automated fiber quantification (AFQ). In addition, mediation analysis was performed to explore the effects of the amygdala-frontal circuit on the relationship between depressive symptoms and cognitive function. We found decreased bilateral amygdala FC with the inferior frontal gyrus (IFG) in the ADD group compared to the ADND and HC groups. Moreover, FA in the left frontal UF (nodes 64-97) was significantly lower in the ADD group than ADND group. Notably, amygdala-based FC with IFG and the left frontal UF FA mediated the relationship between depressive symptoms and cognitive function in ADD, with mediating effects ranging between 15 and 18%. Our study is the first to demonstrate the mediating effect of functional and microstructural abnormalities in the amygdala-frontal circuit in ADD. The findings suggest that the amygdala-frontal circuit may underlie emotional dysregulation in ADD, providing potential targets for treatment strategies.

Alzheimer's Disease and Neurosyphilis: Meaningful Commonalities and Differences of Clinical Phenotype and Pathophysiological Biomarkers

BACKGROUND

Neurosyphilis-associated cognitive and behavioral impairment- historically coined as "general paralysis of the insane"- share clinical and neuroradiological features with the neurodegenerative disease spectrum, in particular Alzheimer's disease (AD). Anatomopathological similarities have been extensively documented, i.e., neuronal loss, fibrillary alterations, and local amyloid-β deposition. Consequently, accurate classification and timely differential diagnosis may be challenging.

OBJECTIVE

To describe clinical, bio-humoral, brain MRI, FDG-PET, and amyloid-PET features in cases of neurosyphilis with an AD-like phenotypical presentation, as well as clinical outcome in terms of response to antibiotic therapy.

METHODS

We selected the studies comparing patients with AD and with neurosyphilis associated cognitive impairment, to investigate candidate biomarkers classifying the two neurological diseases.

RESULTS

The neuropsychological phenotype of general paralysis, characterized by episodic memory impairment and executive disfunction, substantially mimics clinical AD features. Neuroimaging often shows diffuse or medial temporal cortical atrophy, thus contributing to a high rate of misdiagnosis. Cerebrospinal fluid (CSF)-based analysis may provide supportive diagnostic value, since increased proteins or cells are often found in neurosyphilis, while published data on pathophysiological AD candidate biomarkers are controversial. Finally, psychometric testing using cross-domain cognitive tests, may highlight a wider range of compromised functions in neurosyphilis, involving language, attention, executive function, and spatial ability, which are atypical for AD.

CONCLUSION

Neurosyphilis should be considered a potential etiological differential diagnosis of cognitive impairment whenever imaging, neuropsychological or CSF features are atypical for AD, in order to promptly start antibiotic therapy and delay or halt cognitive decline and disease progression.

Disrupted topological organization of functional brain networks in Alzheimer's disease patients with depressive symptoms

BACKGROUND

Depression is a common symptom of Alzheimer's disease (AD), but the underlying neural mechanism is unknown. The aim of this study was to explore the topological properties of AD patients with depressive symptoms (D-AD) using graph theoretical analysis.

METHODS

We obtained 3-Tesla rsfMRI data from 24 D-AD patients, 20 non-depressed AD patients (nD-AD), and 20 normal controls (NC). Resting state networks were identified using graph theory analysis. ANOVA with a two-sample t-test post hoc analysis in GRETNA was used to assess the topological measurements.

RESULTS

Our results demonstrate that the three groups show characteristic properties of a small-world network. NCs showed significantly larger global and local efficiency than D-AD and nD-AD patients. Compared with nD-AD patients, D-AD patients showed decreased nodal centrality in the pallidum, putamen, and right superior temporal gyrus. They also showed increased nodal centrality in the right superior parietal gyrus, the medial orbital portion of the right superior frontal gyrus, and the orbital portion of the right superior frontal gyrus. Compared with nD-AD patients, NC showed decreased nodal betweenness in the right superior temporal gyrus, and increased nodal betweenness in medial orbital part of the right superior frontal gyrus.

CONCLUSIONS

These results indicate that D-AD is associated with alterations of topological structure. Our study provides new insights into the brain mechanisms underlying D-AD.

BACE1 and Other Alzheimer's-Related Biomarkers in Cerebrospinal Fluid and Plasma Distinguish Alzheimer's Disease Patients from Cognitively-Impaired Neurosyphilis Patients

BACKGROUND

Patients with spirochetal infection, which causes neurosyphilis (NS) and at a later stage general paresis of the insane (GPI), present with brain pathology features of Alzheimer's disease (AD). However, the relationships among these illnesses regarding biomarker levels are still unclear.

OBJECTIVE

To explore biomarker levels in NS and GPI compared with those in AD and the relationship between biomarker levels and cognitive function in NS and GPI.

METHODS

Levels of neurogranin (NGRN) and β-amyloid precursor protein cleaving enzyme (BACE1) in cerebrospinal fluid (CSF)/plasma, together with amyloid-β 1-40 (Aβ40), Aβ42, and total tau in the CSF of 23 AD patients, 55 GPI patients, and 13 NS patients were measured. Patients were classified into none-to-mild, moderate, and severe stages of cognitive impairment.

RESULTS

Levels of CSF NGRN, BACE1, and tau as well as plasma BACE1 levels were significantly different among groups. In the none-to-mild stage, plasma BACE1 levels correlated with the protein levels in CSF and were significantly increased in AD patients versus GPI patients. The CSF tau levels in AD patients were significantly increased versus GPI patients in the moderate and severe stages. Pooling data from GPI and NS patients, both CSF tau and plasma NGRN levels correlated with cognitive scale scores.

CONCLUSION

GPI and NS patients might have different biomarker level patterns compared to AD patients. While plasma BACE1 could be a promising early biomarker for distinguishing AD from GPI, CSF tau and plasma NGRN levels might be valuable in indications of cognitive function in pooled NS populations.

Neuropsychiatric Features of Neurosyphilis: Frequency, Relationship with the Severity of Cognitive Impairment and Comparison with Alzheimer Disease

BACKGROUND

The pattern of neuropsychiatric features of patients with neurosyphilis and the impact of the severity of cognitive impairment on neuropsychiatric syndromes are unknown.

OBJECTIVE

We aim to assess the neuropsychiatric features of patients with neurosyphilis, and compare the impact of the severity of cognitive impairment on the neuropsychiatric syndromes between neurosyphilis and Alzheimer disease (AD).

METHODS

Neuropsychiatric symptoms and the degree of cognitive impairment were assessed in a case-control study of 91 neurosyphilis, 162 AD, 157 mild cognitive impairment, and 139 normal controls by the Neuropsychiatric Inventory (NPI) scale and Clinical Dementia Rating scale, respectively. Factor analysis was performed on the 12 NPI items.

RESULTS

Factor analysis showed that patients with neurosyphilis showed more severe neuropsychiatric syndromes at the dementia stage than those neurosyphilis patients at the mild cognitive impairment stage, while neuropsychiatric manifestations were equally common among the different stages of dementia (all p < 0.05). Frontal lobe syndrome was more severe in patients with neurosyphilis than in patients with AD from the early mild cognitive impairment stage to the moderate dementia stage (all p < 0.01).

CONCLUSIONS

Patients with neurosyphilis show different patterns of neuropsychiatric syndromes at the mild cognitive impairment and dementia stages, and differ from patients with AD.

Frequency of Depressive Syndromes in Elderly Individuals with No Cognitive Impairment, Mild Cognitive Impairment, and Alzheimer's Disease Dementia in a Memory Clinic Setting

AIMS

The aims of this study were to investigate the frequency of various depressive syndromes in elderly individuals with no cognitive impairment (NC), mild cognitive impairment (MCI), and Alzheimer's disease dementia (AD) in a memory clinic setting, and then to test whether severe and milder forms of depressive syndromes are differentially associated with the cognitive groups.

METHODS

For 216 NC, 478 MCI, and 316 AD subjects, we investigated the frequency of depressive syndromes, defined by three different categories: major and minor depressive disorder (MaDD and MiDD) according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, as well as depression according to the National Institute of Mental Health provisional diagnostic criteria for depression in Alzheimer's disease (NIMH-dAD).

RESULTS

The frequency of MaDD did not show any significant difference among NC, MCI, and AD. In contrast, the frequencies of MiDD and NIMH-dAD were higher than those of MaDD and showed significant group differences with a gradual increase from NC to AD.

CONCLUSION

The findings suggest that the degenerative process of Alzheimer's disease contributes to the occurrence of mild depressive conditions, but not to severe depression.

Micro-structural white matter abnormalities in type 2 diabetic patients: a DTI study using TBSS analysis

INTRODUCTION

Patients with type 2 diabetes mellitus (T2DM) have usually been found cognitive impairment associated with brain white matter (WM) abnormalities. However, findings have varied across studies, and any potential relationship with Alzheimer's disease (AD) remains unclear. The aim of this study was to assess the whole-brain WM integrity of T2DM patients and to compare our findings with those of published AD cases.

METHODS

In this study, we used diffusion tensor imaging (DTI) combined with tract-based spatial statistics (TBSS) to investigate whole-brain WM abnormalities in 48 T2DM patients and 48 healthy controls. The effects of age and gender were also evaluated.

RESULTS

In our study, significantly decreasing FA and increasing MD and DA values (P<0.05) were found in some WM regions closely related to the default mode network (DMN), including cingulum, the right frontal lobe involving the right uncinate fasciculus (UF), bilateral parietal lobes involving the superior longitudinal fasciculus (SLF) and the inferior longitudinal fasciculus (ILF), and the right middle temporal gyrus (MTG) involving the UF and the ILF. We also found abnormalities in the thalamus involving the fornix (FX), anterior thalamic radiation (ATR), and posterior thalamic radiation (PTR). The damaged regions above are similar to those found in patients with AD, as reported in previous studies.

CONCLUSION

The present study not only provides useful information about the WM regions and tracts affected by T2DM but also offers insight into the underlying neuropathological process in T2DM patients and the relationship between T2DM and AD.