Analysis among cognitive profiles and gray matter volume in newly diagnosed Parkinson's disease with mild cognitive impairment

Grey matter loss across deteriorating cognitive stages in Parkinson's disease

The purpose of the present study was to depict the pattern of grey matter (GM) abnormalities in patients with Parkinson's disease (PD) and various stages of cognitive decline. GM changes were investigated with the use of voxel-based morphometry in three age-matched groups consisted of PD patients with normal cognition (PD-NC, n = 20), mild cognitive impairment (PD-MCI, n = 20) and dementia (PDD, n = 21). The Parkinson's disease-cognitive rating scale (PD-CRS) was used for the neuropsychological assessment of the subjects and to define patient groups. GM atrophy was observed in the PD-MCI group in right middle and inferior temporal gyri and in the PDD group in right thalamus and hippocampus both compared to PD-NC group. Regression analyses retrieved significant associations among total, cortical, and subcortical PD-CRS scores and GM volume in multiple areas, with an exceptionally stable finding being the correlation of striatal atrophy with deteriorating cognitive function. Significant associations were also observed between GM volume in specific regions and the performance of patients in particular PD-CRS items. The study findings reveal a central role of striatal atrophy in the PD-related cognitive decline. Degenerative changes in temporal regions could contribute to MCI, while hippocampal and thalamic atrophy are proposed to accompany the transition to dementia.

Changes of brain structure and structural covariance networks in Parkinson's disease with different sides of onset

Background

Parkinson's disease (PD) typically presents with unilateral symptoms in early stages, starting on one side and progressing, with the onset side showing more severe motor symptoms even after bilateralization. This asymmetry may reflect complex interactions among multiple brain regions and their network connections. In this study, we aimed to use surface-based morphometry (SBM) and structural covariance networks (SCNs) to investigate the differences in brain structure and network characteristics between patients with left-onset PD (LPD) and right-onset PD (RPD).

Methods

A total of 51 LPD and 49 RPD patients were recruited. Clinical assessments included the Unified Parkinson's Disease Rating Scale motor section, Hoehn and Yahr stage, Mini-Mental State Examination, Parkinson's Disease Questionnaire, and Beck Depression Inventory. All participants underwent 3 T structural MRI. FreeSurfer was used to perform vertex-wise comparisons of cortical surface area (CSA) and cortical thickness (CT), whereas the Brain Connectivity Toolbox was implemented to construct and analyze the structural covariance networks.

Results

In patients with LPD, we found reduced CSA in the right supramarginal gyrus (SMG), right precuneus (PCUN), left inferior parietal lobule (IPL), and left lingual gyrus (LING) compared to RPD, while no significant differences in CT were found between the two groups. The CSA of the right PCUN showed a significant positive correlation with MMSE score in LPD patients. In our SCNs analysis, LPD patients exhibited increased normalized characteristic path length and decreased small-world index in CSA-based networks, while in CT-based networks, they showed increased small-world index and global efficiency compared to RPD. No significant differences in nodal characteristics were observed in either CSA-based or CT-based networks between the two groups.

Conclusion

In patients with LPD, reductions in CSA observed in the right PCUN, right SMG, left IPL, and left LING may be associated with cognitive impairments and hallucinations among non-motor symptoms of PD. Additionally, the SCNs of LPD and RPD patients show significant differences in global topology, but regional node characteristics do not reflect lateralization differences. These findings offer new insights into the mechanisms of symptom lateralization in PD from the perspective of brain regional structure and network topology.

The role of Apolipoprotein E4 on cognitive impairment in Parkinson's disease and Parkinsonisms

Cognitive impairment is a prevalent non-motor symptom of Parkinson's disease (PD), increasing the risk of dementia as the disease progresses. Despite its clinical significance, the etiology of cognitive impairment in PD remains unclear. Apolipoprotein E4 (APOE4), a well-known genetic risk factor of Alzheimer's disease, has been studied for its potential role in PD-related cognitive impairment. However, findings have been conflicting and thus inconclusive, highlighting a need to critically evaluate the current research. Several studies using neuroimaging modalities have explored the brains of individuals with PD and atypical parkinsonian disorders who have APOE4. Some of these studies have identified distinct neuropathological changes that have been previously reported to be associated with cognitive impairments in those with Parkinsonisms. Here, we review the role of APOE4 on cognitive impairment in PD and atypical Parkinsonisms using neuroimaging evidence. We will examine how APOE4 may contribute to pathological changes within the brain and its association with cognitive impairment.

The contribution of white matter changes to clinical phenotype in progressive supranuclear palsy

White matter hyperintensities (WMH) are considered magnetic brain imaging (MRI) biomarkers of cerebral small vessel disease but their clinical role in neurodegenerative-related disorders is poorly understood. This study describes the distribution of WMH on brain MRI in Progressive Supranuclear Palsy (PSP) in comparison with Parkinson's disease (PD) and explores their possible impact on disease's features. Sixty PSP and 33 PD patients were included. Motor symptoms, cardiovascular risk factors and the age-related white matter changes (ARWMC) score was computed to rate WMH for both groups. Pearson's correlation and linear or logistic regression analysis were used to check for relationships between ARWMC and PSP clinical scores. The mean (standard deviation) ARWMC total score in the PSP cohort was 4.66 (3.25). Any degree of WMH was present in 68% of PSP (ARWMC +). Compared to ARWMC-, ARWMC + did not have greater disease severity or more cardiovascular risk factors. WMH were frequently localized in fronto-parietal lobes and were mild in severity. Linear regression analysis showed that ARWMC total score was related to the PSP-rating scale, irrespective of age, disease duration and the Charlson modified comorbidity index. Logistic regression analysis confirmed that ARWMC total score was related to the use of wheelchair, irrespective of above-mentioned covariates. Vascular risk factors as well as severity and distribution of WMH did not have an impact on the PSP phenotype. No differences were found with PD patients. Our results suggest that WMH in PSP might be markers of neurodegenerative-related pathology rather than being simple expression of atherosclerotic cerebrovascular changes.

The role of immune and inflammatory-related indicators in cognitive dysfunction and disease severity in patients with parkinson's disease

We aimed to explore the role of immune and inflammatory indicators in cognitive dysfunction and disease severity in patients with Parkinson's disease (PD). A total of 123 patients with Parkinson's disease were enrolled in the PD group and 49 healthy volunteers in the control group. The patients with PD were further divided into 2 subgroups by evaluating cognitive function using the Montreal Cognitive Assessment (MoCA) and Mini-Mental State Examination (MMSE): the normal cognitive function (PD-NCI) group and the mild cognitive impairment (PD-MCI) group. Moreover, the PD patients were also divided into 2 subgroups using the defined scale of the Hoehn and Yahr (H-Y) stage: the early-stage group and the middle- and late-stage group. Immune and inflammatory indicators, including serum Aβ1-42, Tau, CD4+, CD8+, CD3+, B lymphocytes cell, NK cell, Th17 cell, Treg cell, IL-6, IL-17, and TNF-α levels, were evaluated and analyzed to explore the potential correlation with the cognitive dysfunction and disease severity of PD. Among the 123 PD patients, 60 (48.8%) were diagnosed with mild cognitive impairment. Aβ1-42, CD4+, CD8+, CD3+, and Treg levels observed in the PD-NCI group were lower than the control group (P < 0.001), while higher than the PD-MCI group (P < 0.001). The levels of Tau, Th17, IL-6, IL-17, and TNF-α observed in the PD-NCI group were higher than the control group (P < 0.001), while lower than in the PD-MCI group (P < 0.01). Using the same method, the results of the early-stage group and the middle- and the late-stage group were the same as above. Logistic regression analysis and ROC curve estimation were performed and indicated that the variation of Tau, CD8+, Treg, TNF-α levels was associated with cognitive decline in PD patients, and may serve as markers of PD onset. Furthermore, the variation of Aβ1-42, IL-6, and TNF-α levels was found to correlate with the disease severity of PD. The immune and inflammatory-related indicators may represent an important factor in the pathogenesis of PD, cognitive dysfunction, and disease severity. The variation of Tau protein, CD8+, Treg, and TNF-α levels are associated with the cognitive dysfunction of PD, which may be considered as onset markers. Moreover, the variation of Aβ1-42, IL-6, and TNF-α levels can predict the progression of PD.

Altered functional connectivity of the primary motor cortex in tremor dominant and postural instability gait difficulty subtypes of early drug-naive Parkinson's disease patients

Background

The primary motor cortex (M1) is an important hub in the motor circuitry of Parkinson's disease (PD), but the subregions' function and their correlation to tremor dominant (TD) and postural instability and gait disturbance (PIGD) with PD remain unclear. This study aimed to determine whether the functional connectivity (FC) of the M1 subregions varied between the PD and PIGD subtypes.

Methods

We recruited 28 TD patients, 49 PIGD patients, and 42 healthy controls (HCs). M1 was divided into 12 regions of interest using the Human Brainnetome Atlas template to compare FC among these groups.

Results

Compared with HCs, TD and PIGD patients exhibited increased FC between the left upper limb region (A4UL_L) and the right caudate nucleus (CAU)/left putamen (PUT), between the right A4UL (A4UL_R) and the left anterior cingulate and paracingulate gyri (ACG)/bilateral cerebellum4_5 (CRBL4_5)/left PUT/right CAU/left supramarginal gyrus/left middle frontal gyrus (MFG), as well as decreased connectivity between the A4UL_L and the left postcentral gyrus and the bilateral cuneus, and between the A4UL_R and the right inferior occipital gyrus. TD patients showed increased FC between the right caudal dorsolateral area 6 (A6CDL_R) and the left ACG/right MFG, between the A4UL_L and the right CRBL6/right middle frontal gyrus, orbital part/bilateral inferior frontal gyrus, and orbital part (ORBinf), and between the A4UL_R and the left ORBinf/right MFG/right insula (INS). PIGD patients displayed increased connectivity between the A4UL_L and the left CRBL4_5. Compared with PIGD patients, TD patients exhibited increased connectivity between the A6CDL_R and the left ACG/right MFG and between the A4UL_R and the left ACG/left ORBinf/right INS/right MFG. Furthermore, in TD and PIGD groups, the FC strength between the A6CDL_R and right MFG was negatively correlated with PIGD scores, while the FC strength between the A4UL_R and left ORBinf/right INS was positively correlated with TD scores and tremor scores.

Conclusion

Our results demonstrated that early TD and PIGD patients share some common injury and compensatory mechanisms. TD patients occupied more resources in the MFG, ORBinf, INS, and ACG, which can be used as biomarkers to distinguish them from PIGD patients.

White and gray matter alterations in de novo PD patients: which matter most?

OBJECTIVES

This paper aimed to identify white matter (WM) and gray matter (GM) abnormalities in a sample of early PD patients, and their correlations with motor and non-motor symptom severity.

METHODS

We enrolled 62 de novo PD patients and 31 healthy subjects. Disease severity and non-motor symptom burden were assessed by the Unified Parkinson's Disease Rating Scale part III and the Non-Motor Symptoms Scale, respectively. Cognitive performance was assessed using Montreal Cognitive Assessment and Frontal Assessment Battery. All subjects underwent a 3-Tesla MRI protocol. MRI analyses included tract-based spatial statistics, cortical thickness, and subcortical and cerebellar volumetry.

RESULTS

In comparison to control subjects, PD patients exhibited lower fractional anisotropy and higher mean, axial, and radial diffusivity in most WM bundles, including corticospinal tracts, the internal and external capsule, the anterior and posterior thalamic radiations, the genu and body of the corpus callosum, cerebellar peduncles, and superior and inferior longitudinal and fronto-occipital fasciculi. Correlations between Montreal Cognitive Assessment scores and fractional anisotropy values in the right posterior thalamic radiation, left superior corona radiata, right inferior-fronto-occipital fasciculus, left inferior longitudinal fasciculus, bilateral anterior thalamic radiations, and bilateral superior longitudinal fasciculi were found. Smaller cerebellar volumes in early PD patients in the left and right crus I were also found. No GM changes were present in subcortical or cortical regions.

CONCLUSION

The combined evaluation of WM and GM in the same patient sample demonstrates that WM microstructural abnormalities precede GM structural changes in early PD patients.

Neural basis of impaired narrative discourse comprehension in prodromal and mild dementia with lewy bodies

Narrative discourse (ND) comprehension is a complex task that implies not only linguistic abilities but also other cognitive abilities, including efficient executive functioning. An executive dysfunction has been described in dementia with Lewy bodies (DLB) from the early stage. Here, we question the link between executive dysfunction in DLB and narrative comprehension. The aim of our study was to evaluate ND comprehension and to investigate the neuroanatomical basis for its impairment in the early stage of DLB. DLB patients (N = 26) and controls (N = 19) underwent the ND comprehension test of the Montreal Protocol for Evaluation of Communication (MEC). An additional, qualitative analysis was conducted on their verbal productions. Cognitive tests assessing verbal episodic memory, executive functions, naming and oral syntactic comprehension were also performed. Brain gray matter correlates of the ND comprehension test were examined using voxel-based morphometry (VBM). An ND comprehension impairment was found for prodromal and mild DLB patients as compared to controls. These difficulties were correlated with the Frontal Assessment Battery (FAB) score. ND comprehension impairment in DLB was further characterized by a deficit in the organization and the logic of the discourse. Moreover, VBM analysis revealed a correlation between striatal gray matter volumes and DLB patients’ ability to extract and organize relevant information (p < 0.05, FDR correction, cluster level). The ND comprehension impairment in DLB patients could be related to their executive dysfunction through a deficit of information selection and organization that correlates with the volumetric reduction of striatal gray matter.

Cognitive Deficit and Aberrant Intrinsic Brain Functional Network in Early-Stage Drug-Naive Parkinson's Disease

BACKGROUND

Although cognitive deficit is a common non-motor symptom of Parkinson's disease (PD), the mechanism and valid biomarkers of it have not been identified. To our best knowledge, this was the first study to investigate the intrinsic dysconnectivity pattern of whole-brain functional networks in early-stage drug-naive (ESDN) PD patients and its association with cognitive deficit of PD using voxel-wise Degree Centrality (DC) approach.

METHODS

A total of 53 ESDN PD patients and 53 healthy controls (HC) were recruited. Resting-state fMRI (rs-fMRI) data were acquired, and voxel-wise DC approach was applied. Electrophysiological testing at P300 amplitude was recorded. The Montreal Cognitive Assessment (MoCA) was conducted to evaluate cognitive performance.

RESULTS

ESDN PD patients had lower MoCA scores and P300 amplitudes, but higher P300 latency, than HC (all p < 0.0001). PD patients displayed higher DC in the right inferior frontal gyrus (IFG), left medial frontal gyrus (MFG) and left precentral gyrus (PreCG); but lower DC in the left inferior parietal lobule (IPL), left inferior temporal gyrus (ITG), right occipital lobe, and right postcentral gyrus (PoCG) (pBonferroni correction < 0.0001). Interestingly, the DC values of left MFG, right PoCG and right occipital lobe were negatively associated with P300 latency but positively associated with P300 amplitudes and MoCA scores (all pBonferroni correction < 0.0001).

CONCLUSIONS

Our results indicate the cognitive deficit and abnormal intrinsic brain functional network in ESDN PD patients. The damage of Default Mode Network (DMN) may be contributes to the pathogenesis of cognitive dysfunction in ESDN PD.

Hippocampal volume is related to olfactory impairment in Parkinson's disease

BACKGROUND AND PURPOSE

Recent evidence has suggested that hyposmia in patients with Parkinson's disease (PD) may be due to impaired central processing. Furthermore, the hippocampus has been regarded as a critical structure linking olfactory impairment and cognitive impairment in PD patients. This study aimed to identify significant structural alterations of the hippocampus in PD patients with hyposmia, and to determine whether these structural changes are significantly associated with olfactory impairment severity.

METHODS

Eighteen idiopathic PD patients with hyposmia and 18 age- and sex-matched PD patients without hyposmia were enrolled. Hippocampal volume and its subfields were measured using FreeSurfer software and compared between hyposmic and normosmic PD patients. We also compared hippocampal substructures' volumes and correlated the hippocampal volumes with hyposmia severity.

RESULTS

PD patients with hyposmia had significantly smaller hippocampal volumes. Among the three components of the hippocampus, the hippocampal body showed a markedly lower volume, which correlated significantly with the cross-cultural smell identification test score that represents olfactory function status. Hippocampal subfield analysis showed that substructures (subiculum, molecular layer) that constitute the hippocampal body showed the most significant volume difference.

CONCLUSIONS

We suggest that atrophy of the bilateral hippocampus implies underlying problems in the central olfaction process in PD patients. In particular, the hippocampus might not only play a critical role in olfaction but could also be important for elucidating possible mechanisms of broad nonmotor symptoms in PD patients.

Neuroanatomical changes in early Parkinson's disease with mild cognitive impairment: a VBM study; the Parkinson's Disease Cognitive Impairment Study (PaCoS)

INTRODUCTION

Mild cognitive impairment (MCI) is common in Parkinson's disease (PD), but the underlying pathological mechanism has not been fully understood. Voxel-based morphometry could be used to evaluate regional atrophy and its relationship with cognitive performances in early PD-MCI.

PATIENTS AND METHODS

One hundred and six patients with PD were recruited from a larger cohort of patients, the Parkinson's Disease Cognitive Impairment Study (PaCoS). Subject underwent a T1-3D MRI and a complete clinical and neuropsychological evaluation. Patients were divided into PD with normal cognition (PD-NC) and PD-MCI according to the MDS level II criteria-modified for PD-MCI. A subgroup of early patients with short disease duration (≤ 2 years) was also identified. VBM analysis between PD-NC and PD-MCI and between early PD-NC and PD-MCI was performed using two-sample t tests with whole-brain statistical threshold of p < 0.001 uncorrected in the entire PD group and p < 0.05 FWE inside ROIs, in the early PD.

RESULTS

Forty patients were diagnosed with MCI and 66 were PD-NC. PD-MCI patients showed significant gray matter (GM) reduction in several brain regions, including frontal gyrus, precuneus, angular gyrus, temporal lobe, and cerebellum. Early PD-MCI showed reduction in GM density in superior frontal gyrus and cerebellum. Moreover, correlation analysis between neuropsychological performances and GM volume of early PD-MCI patients showed associations between performances of Raven and superior frontal gyrus volume, Stroop time and inferior frontal gyrus volume, accuracy of Barrage and volume of precuneus.

CONCLUSION

The detection of frontal and cerebellar atrophy, even at an early stage, could be used as an early marker of PD-related cognitive impairment.

Association of Hippocampal Subfields, CSF Biomarkers, and Cognition in Patients With Parkinson Disease Without Dementia

OBJECTIVE

To examine whether hippocampal volume loss is primarily associated with cognitive status or pathologic β-amyloid 1-42 (Aβ42) levels, this study compared hippocampal subfield volumes between patients with Parkinson disease (PD) with mild cognitive impairment (PD-MCI) and without cognitive impairment (PD-CN) and between patients with low and high Aβ42 levels, in addition exploring the relationship among hippocampal subfield volumes, CSF biomarkers (Aβ42, phosphorylated and total tau), neuropsychological tests, and activities of daily living.

METHODS

Forty-five patients with PD without dementia underwent CSF analyses and MRI as well as comprehensive motor and neuropsychological examinations. Hippocampal segmentation was conducted using FreeSurfer image analysis suite 6.0. Regression models were used to compare hippocampal subfield volumes between groups, and partial correlations defined the association between variables while controlling for intracranial volume (ICV).

RESULTS

Linear regressions revealed cognitive group as a statistically significant predictor of both the hippocampal-amygdaloid transition area (HATA; β = -0.23, 95% CI -0.44 to -0.02) and the cornu ammonis 1 region (CA1; β = -0.28, 95% confidence interval [CI] -0.56 to -0.02), independent of disease duration and ICV, with patients with PD-MCI showing significantly smaller volumes than PD-CN. In contrast, no subfields were predicted by Aβ42 levels. Smaller hippocampal volumes were associated with worse performance on memory, language, spatial working memory, and executive functioning tests. The subiculum was negatively correlated with total tau levels (r = -0.37, 95% CI -0.60 to -0.09).

CONCLUSION

Cognitive status, but not CSF Aβ42, predicted hippocampal volumes, specifically the CA1 and HATA. Hippocampal subfields were associated with various cognitive domains, as well as with tau pathology.

Brain MRI Reveals Ascending Atrophy in Parkinson's Disease Across Severity

Models which assess the progression of Lewy pathology in Parkinson's disease have proposed ascending spread in a caudal-rostral pattern. In-vivo human evidence for this theory is limited, in part because there are no biomarkers that allow for direct assessment of Lewy pathology. Here, we measured neurodegeneration via MRI, an outcome which may serve as a proxy for a more direct assessment of ascending models using a combination of (1) MRI-based measures of gray matter density and (2) regions of interest (ROIs) corresponding to cortical and subcortical loci implicated in past MRI and stereological studies of Parkinson's disease. Gray matter density was measured using brain MRI voxel-based morphometry from three cohorts: (1) early Parkinson's disease, (2) more advanced Parkinson's disease and (3) healthy controls. Early Parkinson's disease patients (N = 228, mean age = 61.9 years, mean disease duration = 0.6 years) were newly diagnosed by the Parkinson's Progression Markers Initiative (PPMI). Advanced Parkinson's disease patients (N = 136, mean age = 63.5 years, mean disease duration = 8.0 years) were collected retrospectively from a local cohort undergoing evaluation for functional neurosurgery. Control subjects (N = 103, mean age = 60.2 years) were from PPMI. Comparative analyses focused on gray matter regions ranging from deep gray subcortical structures to the neocortex. ROIs were defined with existing probabilistic cytoarchitectonic brain maps. For subcortical regions of the basal forebrain, amygdala, and entorhinal cortex, advanced Parkinson's disease patients had significantly lower gray matter density when compared to both early Parkinson's disease and healthy controls. No differences were seen in neocortical regions that are "higher" in any proposed ascending pattern. Across early and advanced Parkinson's disease, gray matter density from nearly all subcortical regions significantly decreased with disease duration; no neocortical regions showed this effect. These results demonstrate that atrophy in advanced Parkinson's patients compared to early patients and healthy controls is largely confined to subcortical gray matter structures. The degree of atrophy in subcortical brain regions was linked to overall disease duration, suggesting an organized pattern of atrophy across severity.

Neural correlates of distinct cognitive phenotypes in early Parkinson's disease

OBJECTIVE

Cognitive decline is common in Parkinson's disease (PD), but changes can occur in a variety of cognitive domains. The lack of a single cognitive phenotype complicates diagnosis and tracking. In an earlier study we used a data-driven approach to identify distinct cognitive phenotypes of early PD. Here we identify the morphometric brain differences between those different phenotypes compared with cognitively normal PD participants.

METHODS

Six different cognitive classes were included (Weak, Typical, Weak-Visuospatial/Strong-Memory, Weak-Visuospatial, Amnestic, Strong). Structural differences between each class and the Typical class were assessed by deformation-based morphometry.

RESULTS

The different groups evidenced different patterns of atrophy. Weak class had frontotemporal and insular atrophy; Weak-Visuospatial/Strong-Memory class had frontotemporal, insular, parietal, and putamen atrophy; Weak-Visuospatial class had Rolandic operculum; Amnestic class had left frontotemporal, occipital, parietal and insular atrophy when compared to the Typical class. The Strong class did not have any atrophy but had significant differences in left temporal cortex in comparison to the Typical class.

CONCLUSIONS

Structural neuroimaging differences are evident in PD patients with distinct cognitive phenotypes even very early in the disease process prior to the emergence of frank cognitive impairment. Future studies will elucidate whether these have prognostic value in identifying trajectories toward dementia, or if they represent groups sensitive to different treatments.

Differential Progression of Regional Hippocampal Atrophy in Aging and Parkinson's Disease

Hippocampal subfields have different vulnerability to the degenerative processes related to aging, amnestic mild cognitive impairment (MCI) and Alzheimer’s disease (AD), but the temporal evolution in Parkinson’s disease (PD) is unknown. The purposes of the current work are to describe regional hippocampal changes over time in a sample of PD patients classified according to their baseline cognitive status and to relate these changes to verbal memory loss. T1-weighted images and verbal memory assessment were obtained at two separate time points (3.8 ± 0.4 years apart) from 28 PD with normal cognition (PD-NC), 16 PD with MCI (PD-MCI) and 21 healthy controls (HCs). FreeSurfer 6.0 automated pipeline was used to segment the hippocampus into 12 bilateral subregions. Memory functions were measured with Rey’s Auditory Verbal learning test (RAVLT). We found significant reductions in cornu ammonis 1 (CA1) over time in controls as well as in PD subgroups. Right whole-hippocampal volumes showed time effects in both PD groups but not in controls. PD-NC patients also displayed time effects in the left hippocampal tail and right parasubiculum. Regression analyses showed that specific hippocampal subfield volumes at time 1 predicted almost 60% of the variability in RAVLT delayed-recall score decline. Changes in several hippocampal subregions also showed predictive value for memory loss. In conclusion, CA1 changes in PD were similar to those that occur in normal aging, but PD patients also had more decline in both anterior and posterior hippocampal segments with a more pronounced atrophy of the right hemisphere. Hippocampal segments are better predictors of changes in memory performance than whole-hippocampal volumes.

Can neuroimaging predict dementia in Parkinson's disease?

Dementia in Parkinson's disease affects 50% of patients within 10 years of diagnosis but there is wide variation in severity and timing. Thus, robust neuroimaging prediction of cognitive involvement in Parkinson's disease is important: (i) to identify at-risk individuals for clinical trials of potential new treatments; (ii) to provide reliable prognostic information for individuals and populations; and (iii) to shed light on the pathophysiological processes underpinning Parkinson's disease dementia. To date, neuroimaging has not made major contributions to predicting cognitive involvement in Parkinson's disease. This is perhaps unsurprising considering conventional methods rely on macroscopic measures of topographically distributed neurodegeneration, a relatively late event in Parkinson's dementia. However, new technologies are now emerging that could provide important insights through detection of other potentially relevant processes. For example, novel MRI approaches can quantify magnetic susceptibility as a surrogate for tissue iron content, and increasingly powerful mathematical approaches can characterize the topology of brain networks at the systems level. Here, we present an up-to-date overview of the growing role of neuroimaging in predicting dementia in Parkinson's disease. We discuss the most relevant findings to date, and consider the potential of emerging technologies to detect the earliest signs of cognitive involvement in Parkinson's disease.

Structural and Functional Brain Patterns of Non-Motor Syndromes in Parkinson's Disease

Parkinson’s disease (PD) is a common, progressive and multisystem neurodegenerative disorder characterized by motor and non-motor symptoms. Advanced magnetic resonance imaging, positron emission tomography, and functional magnetic resonance imaging can render the view toward understanding the neural basis of these non-motor syndromes, as they help to understand the underlying pathophysiological abnormalities. This review provides an up-to-date description of structural and functional brain alterations in patients with PD with cognitive deficits, visual hallucinations, fatigue, impulsive behavior disorders, sleep disorders, and pain.

Synucleinopathies: common features and hippocampal manifestations

Parkinson's disease (PD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA) are three major synucleinopathies characterized by α-synuclein-containing inclusions in the brains of patients. Because the cell types and brain structures that are affected vary markedly between the disorders, the patients have different clinical manifestations in addition to some overlapping symptoms, which are the basis for differential diagnosis. Cognitive impairment and depression associated with hippocampal dysfunction are frequently observed in these disorders. While various α-synuclein-containing inclusions are found in the hippocampal formation, increasing evidence supports that small α-synuclein aggregates or oligomers may be the real culprit, causing deficits in neurotransmission and neurogenesis in the hippocampus and related brain regions, which constitute the major mechanism for the hippocampal dysfunctions and associated neuropsychiatric manifestations in synucleinopathies.

Fragile X-associated tremor/ataxia syndrome: phenotypic comparisons with other movement disorders

OBJECTIVE

The purpose of this paper is to review the typical cognitive and motor impairments seen in fragile X-associated tremor/ataxia syndrome (FXTAS), essential tremor (ET), Parkinson disease (PD), spinocerebellar ataxias (SCAs), multiple system atrophy (MSA), and progressive supranuclear palsy (PSP) in order to enhance diagnosis of FXTAS patients.

METHODS

We compared the cognitive and motor phenotypes of FXTAS with each of these other movement disorders. Relevant neuropathological and neuroimaging findings are also reviewed. Finally, we describe the differences in age of onset, disease severity, progression rates, and average lifespan in FXTAS compared to ET, PD, SCAs, MSA, and PSP. We conclude with a flow chart algorithm to guide the clinician in the differential diagnosis of FXTAS.

RESULTS

By comparing the cognitive and motor phenotypes of FXTAS with the phenotypes of ET, PD, SCAs, MSA, and PSP we have clarified potential symptom overlap while elucidating factors that make these disorders unique from one another. In summary, the clinician should consider a FXTAS diagnosis and testing for the Fragile X mental retardation 1 (FMR1) gene premutation if a patient over the age of 50 (1) presents with cerebellar ataxia and/or intention tremor with mild parkinsonism, (2) has the middle cerebellar peduncle (MCP) sign, global cerebellar and cerebral atrophy, and/or subcortical white matter lesions on MRI, or (3) has a family history of fragile X related disorders, intellectual disability, autism, premature ovarian failure and has neurological signs consistent with FXTAS. Peripheral neuropathy, executive function deficits, anxiety, or depression are supportive of the diagnosis.

CONCLUSIONS

Distinct profiles in the cognitive and motor domains between these movement disorders may guide practitioners in the differential diagnosis process and ultimately lead to better medical management of FXTAS patients.

Biomarkers for dementia and mild cognitive impairment in Parkinson's disease

Cognitive decline is one of the most frequent and disabling nonmotor features of Parkinson's disease. Around 30% of patients with Parkinson's disease experience mild cognitive impairment, a well-established risk factor for the development of dementia. However, mild cognitive impairment in patients with Parkinson's disease is a heterogeneous entity that involves different types and extents of cognitive deficits. Because it is not currently known which type of mild cognitive impairment confers a higher risk of progression to dementia, it would be useful to define biomarkers that could identify these patients to better study disease progression and possible interventions. In this sense, the identification among patients with Parkinson's disease and mild cognitive impairment of biomarkers associated with dementia would allow the early detection of this process. This review summarizes studies from the past 25 years that have assessed the potential biomarkers of dementia and mild cognitive impairment in Parkinson's disease patients. Despite the potential importance, no biomarker has as yet been validated. However, features such as low levels of epidermal and insulin-like growth factors or uric acid in plasma/serum and of Aß in CSF, reduction of cerebral cholinergic innervation and metabolism measured by PET mainly in posterior areas, and hippocampal atrophy in MRI might be indicative of distinct deficits with a distinct risk of dementia in subgroups of patients. Longitudinal studies combining the existing techniques and new approaches are needed to identify patients at higher risk of dementia. © 2016 International Parkinson and Movement Disorder Society.

Apathy and noradrenaline: silent partners to mild cognitive impairment in Parkinson's disease?

PURPOSE OF REVIEW

Mild cognitive impairment (MCI) is a comorbid factor in Parkinson's disease. The aim of this review is to examine the recent neuroimaging findings in the search for Parkinson's disease MCI (PD-MCI) biomarkers to gain insight on whether MCI and specific cognitive deficits in Parkinson's disease implicate striatal dopamine or another system.

RECENT FINDINGS

The evidence implicates a diffuse pathophysiology in PD-MCI rather than acute dopaminergic involvement. On the one hand, performance in specific cognitive domains, notably in set-shifting and learning, appears to vary with dopaminergic status. On the other hand, motivational states in Parkinson's disease along with their behavioral and physiological indices suggest a noradrenergic contribution to cognitive deficits in Parkinson's disease. Finally, Parkinson's disease's pattern of neurodegeneration offers an avenue for continued research in nigrostriatal dopamine's role in distinct behaviors, as well as the specification of dorsal and ventral striatal functions.

SUMMARY

The search for PD-MCI biomarkers has employed an array of neuroimaging techniques, but still yields divergent findings. This may be due in part to MCI's broad definition, encompassing heterogeneous cognitive domains, only some of which are affected in Parkinson's disease. Most domains falling under the MCI umbrella include fronto-dependent executive functions, whereas others, notably learning, rely on the basal ganglia. Given the deterioration of the nigrostriatal dopaminergic system in Parkinson's disease, it has been the prime target of PD-MCI investigation. By testing well defined cognitive deficits in Parkinson's disease, distinct functions can be attributed to specific neural systems, overcoming conflicting results on PD-MCI. Apart from dopamine, other systems such as the neurovascular or noradrenergic systems are affected in Parkinson's disease. These factors may be at the basis of specific facets of PD-MCI for which dopaminergic involvement has not been conclusive. Finally, the impact of both dopaminergic and noradrenergic deficiency on motivational states in Parkinson's disease is examined in light of a plausible link between apathy and cognitive deficits.