A modern hypothesis: The distinct pathologies of dementia associated with Parkinson's disease versus Alzheimer's disease

BDNF Signaling in Vascular Dementia and Its Effects on Cerebrovascular Dysfunction, Synaptic Plasticity, and Cholinergic System Abnormality

Vascular dementia (VaD) is the second most common type of dementia and is characterized by memory impairment, blood-brain barrier disruption, neuronal cell loss, glia activation, impaired synaptic plasticity, and cholinergic system abnormalities. To effectively prevent and treat VaD a good understanding of the mechanisms underlying its neuropathology is needed. Brain-derived neurotrophic factor (BDNF) is an important neurotrophic factor with multiple functions in the systemic circulation and the central nervous system and is known to regulate neuronal cell survival, synaptic formation, glia activation, and cognitive decline. Recent studies indicate that when compared with normal subjects, patients with VaD have low serum BDNF levels and that BDNF deficiency in the serum and cerebrospinal fluid is an important indicator of VaD. Here, we review current knowledge on the role of BDNF signaling in the pathology of VaD, such as cerebrovascular dysfunction, synaptic dysfunction, and cholinergic system impairment.

Neuroimaging in Parkinson's disease dementia: connecting the dots

Dementia is a common and devastating symptom of Parkinson's disease but the anatomical substrate remains unclear. Some evidence points towards hippocampal involvement but neuroimaging abnormalities have been reported throughout the brain and are largely inconsistent across studies. Here, we test whether these disparate neuroimaging findings for Parkinson's disease dementia localize to a common brain network. We used a literature search to identify studies reporting neuroimaging correlates of Parkinson's dementia (11 studies, 385 patients). We restricted our search to studies of brain atrophy and hypometabolism that compared Parkinson's patients with dementia to those without cognitive involvement. We used a standard coordinate-based activation likelihood estimation meta-analysis to assess for consistency in the neuroimaging findings. We then used a new approach, coordinate-based network mapping, to test whether neuroimaging findings localized to a common brain network. This approach uses resting-state functional connectivity from a large cohort of normative subjects (n = 1000) to identify the network of regions connected to a reported neuroimaging coordinate. Activation likelihood estimation meta-analysis failed to identify any brain regions consistently associated with Parkinson's dementia, showing major heterogeneity across studies. In contrast, coordinate-based network mapping found that these heterogeneous neuroimaging findings localized to a specific brain network centred on the hippocampus. Next, we tested whether this network showed symptom specificity and stage specificity by performing two further analyses. We tested symptom specificity by examining studies of Parkinson's hallucinations (9 studies, 402 patients) that are frequently co-morbid with Parkinson's dementia. We tested for stage specificity by using studies of mild cognitive impairment in Parkinson's disease (15 studies, 844 patients). Coordinate-based network mapping revealed that correlates of visual hallucinations fell within a network centred on bilateral lateral geniculate nucleus and correlates of mild cognitive impairment in Parkinson's disease fell within a network centred on posterior default mode network. In both cases, the identified networks were distinct from the hippocampal network of Parkinson's dementia. Our results link heterogeneous neuroimaging findings in Parkinson's dementia to a common network centred on the hippocampus. This finding was symptom and stage-specific, with implications for understanding Parkinson's dementia and heterogeneity of neuroimaging findings in general.

Association Between Pathology and Electroencephalographic Activity in Parkinson's Disease

INTRODUCTION

The key mechanisms that connect Parkinson's disease pathology with dementia are unclear. We tested the hypothesis that the quantitative spectral electroencephalographic measure, delta bandpower, correlates with Lewy type synucleinopathy on pathological examination in Parkinson's disease. As a corollary hypothesis, we analyzed whether there would be delta bandpower electroencephalographic differences between Parkinson's disease dementia cases with and without pathological criteria for Alzheimer's disease.

METHODS

We used pathological examination results from 44 Parkinson's disease subjects from our brain bank with various degrees of cognitive decline, who had undergone electroencephalography. Pathological grading for Lewy type synucleinopathy, plaques, tangles, and indications of vascular pathology in subcortical and cortical areas were correlated with the most associated electroencephalographic biomarker with Parkinson's disease dementia in our laboratory, delta bandpower. Group differences for all spectral electroencephalographic measures were also analyzed between cases with and without pathological criteria for Alzheimer's disease.

RESULTS

Findings revealed significant correlations between delta bandpower with Lewy type synucleinopathy, whereas indications of Alzheimer's disease or vascular pathology had nonsignificant correlation. The strongest association was with delta bandpower and Lewy type synucleinopathy in the anterior cingulate region. Mean delta bandpower was higher in the group for Parkinson's disease dementia with Alzheimer's disease pathology criteria than without.

CONCLUSIONS

Lewy type synucleinopathy severity appears to be more associated with increased delta bandpower than with Alzheimer's disease pathology or indications of vascular pathology over all cases. However, the presence of Alzheimer's pathology may associate with more cortex physiological disruption in a subset of cases.

Houttuynia cordata Improves Cognitive Deficits in Cholinergic Dysfunction Alzheimer's Disease-Like Models

Cognitive impairment is a result of dementia of diverse causes, such as cholinergic dysfunction and Alzheimer's disease (AD). Houttuynia cordata Thunb. (Saururaceae) has long been used as a traditional herbal medicine. It has biological activities including protective effects against amyloid beta (Aβ) toxicity, via regulation of calcium homeostasis, in rat hippocampal cells. To extend previous reports, we investigated the effects of water extracts of H. cordata herb (HCW) on tauopathies, also involving calcium influx. We then confirmed the effects of HCW in improving memory impairment and neuronal damage in mice with Aβ-induced neurotoxicity. We also investigated the effects of HCW against scopolamine-induced cholinergic dysfunction in mice. In primary neuronal cells, HCW inhibited the phosphorylation of tau by regulating p25/p35 expression in Aβ-induced neurotoxicity. In mice with Aβ-induced neurotoxicity, HCW improved cognitive impairment, as assessed with behavioral tasks, such as novel object recognition, Y-maze, and passive avoidance tasks. HCW also inhibited the degeneration of neurons in the CA3 region of the hippocampus in Aβ-induced neurotoxicity. Moreover, HCW, which had an IC50 value of 79.7 μg/ml for acetylcholinesterase inhibition, ameliorated scopolamine-induced cognitive impairment significantly in Y-maze and passive avoidance tasks. These results indicate that HCW improved cognitive impairment, due to cholinergic dysfunction, with inhibitory effects against tauopathies and cholinergic antagonists, suggesting that HCW may be an interesting candidate to investigate for the treatment of AD.

Comparing clinical profiles in Alzheimer's disease and Parkinson's disease dementia

Background

Greater understanding of differences in baseline impairment and disease progression in patients with Alzheimer's disease (AD) and Parkinson's disease dementia (PDD) may improve the interpretation of drug effects and the design of future studies.

Methods

This was a retrospective analysis of three randomized, double-blind rivastigmine databases (one in PDD, two in AD). Impairment on the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog), Alzheimer's Disease Cooperative Study-Activities of Daily Living (ADCS-ADL) scale, 10-item Neuropsychiatric Inventory (NPI-10) and the ADCS-Clinical Global Impression of Change (CGIC) was compared [standardized difference (Cohen's d), similar if <0.1].

Results

Patients with AD or PDD had similar levels of impairment on the ADAS-cog and NPI-10. Scores on the ADCS-ADL scale (standardized difference = 0.47) and the ADAS-cog memory domain (total, 0.33; items, 0.10-0.58) were higher in AD; PDD patients were more impaired in the language (0.23) and praxis (0.34) domains. AD patients receiving placebo showed greater deterioration on the ADAS-cog (0.14) and improvement on the NPI-10 (0.11) compared with patients with PDD.

Conclusion

Differing patterns of impairment occur in AD and PDD.

Mild cognitive impairment in patients with Parkinson's disease is associated with increased cortical degeneration

Mild cognitive impairment (MCI) can occur early in the course of Parkinson's disease (PD), and its presence increases the risk of developing dementia. Determining the cortical changes associated with MCI in PD, thus, may be useful in predicting the future development of dementia. To address this objective, 37 patients with PD, divided into 2 groups according to the presence or absence MCI (18 with and 19 without) and 16 matched controls, underwent anatomic magnetic resonance imaging. Corticometry analyses were performed to measure the changes in cortical thickness and surface area as well as their correlation with disease duration. Compared with healthy controls, the PD-MCI group exhibited increased atrophy and changes of local surface area in the bilateral occipital, left temporal, and frontal cortices; whereas the PD non-MCI group exhibited only unilateral thinning and decreased surface area in the occipital lobe and in the frontal cortex. In addition, a comparison between the PD-MCI and PD non-MCI groups revealed increased local surface area in the occipital lobe, temporal lobe, and postcentral gyrus for the cognitively impaired patients. It is noteworthy that, in the PD-MCI group, cortical thickness had a significant negative correlation with disease duration in the precentral, supramarginal, occipital, and superior temporal cortices; whereas, in the PD non-MCI group, such a correlation was absent. The findings from this study reveal that, at the same stage of PD evolution, the presence of MCI is associated with a higher level of cortical changes, suggesting that cortical degeneration is increased in patients with PD because of the presence of MCI.

Lack of Genetic Associations of PPAR-γ and PGC-1α with Alzheimer's Disease and Parkinson's Disease with Dementia

Background and Aims

Similar clinical and pathological features have been observed in Alzheimer's disease (AD) and Parkinson's disease with dementia (PDD). Both the peroxisome proliferator-activated receptor-γ (PPAR-γ) gene and the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) gene are candidates modifying the risk for both diseases. The aim of this study was to clarify whether common single nucleotide polymorphisms (SNPs) of the PPAR-γ gene and the PGC-1α gene affect the onset of AD and PDD genetically.

Methods

Four exonic SNPs of both genes (rs1801282 and rs3856806 of the PPAR-γ gene, rs3736265 and rs8192678 of the PGC-1α gene) were genotyped in 171 AD patients, 136 age-matched controls and 53 PDD patients. Haplotype analysis and logistic regression analysis with apolipoprotein E (APO E) status were performed for AD.

Results

There was no statistical difference between AD cases and controls for the 4 SNPs, nor was there any statistical difference between PDD cases and controls for the 4 SNPs. We could not find any synergetic associations between these SNPs, APO E4 and AD.

Conclusions

The 4 SNPs studied here did not influence the risk for AD in a Japanese population. As the number of PDD cases was small, comprehensive genetic studies considering diabetes would be needed.

Alzheimer's disease pattern of brain atrophy predicts cognitive decline in Parkinson's disease

Research suggests overlap in brain regions undergoing neurodegeneration in Parkinson's and Alzheimer's disease. To assess the clinical significance of this, we applied a validated Alzheimer's disease-spatial pattern of brain atrophy to patients with Parkinson's disease with a range of cognitive abilities to determine its association with cognitive performance and decline. At baseline, 84 subjects received structural magnetic resonance imaging brain scans and completed the Dementia Rating Scale-2, and new robust and expanded Dementia Rating Scale-2 norms were applied to cognitively classify participants. Fifty-nine non-demented subjects were assessed annually with the Dementia Rating Scale-2 for two additional years. Magnetic resonance imaging scans were quantified using both a region of interest approach and voxel-based morphometry analysis, and a method for quantifying the presence of an Alzheimer's disease spatial pattern of brain atrophy was applied to each scan. In multivariate models, higher Alzheimer's disease pattern of atrophy score was associated with worse global cognitive performance (β = -0.31, P = 0.007), including in non-demented patients (β = -0.28, P = 0.05). In linear mixed model analyses, higher baseline Alzheimer's disease pattern of atrophy score predicted long-term global cognitive decline in non-demented patients [F(1, 110) = 9.72, P = 0.002], remarkably even in those with normal cognition at baseline [F(1, 80) = 4.71, P = 0.03]. In contrast, in cross-sectional and longitudinal analyses there was no association between region of interest brain volumes and cognitive performance in patients with Parkinson's disease with normal cognition. These findings support involvement of the hippocampus and parietal-temporal cortex with cognitive impairment and long-term decline in Parkinson's disease. In addition, an Alzheimer's disease pattern of brain atrophy may be a preclinical biomarker of cognitive decline in Parkinson's disease.

Magnetic resonance spectroscopic methods for the assessment of metabolic functions in the diseased brain

Magnetic resonance spectroscopy (MRS) is a non-invasive technique that can be used to detect and quantify multiple metabolites. This chapter will review some of the applications of MRS to the study of brain functions. Typically, (1)H-MRS can detect metabolites reflecting neuronal density and integrity, markers of energy metabolism or inflammation, as well as neurotransmitters. The complexity of the proton spectrum has however led to the development of other nuclei-based methods, such as (31)P- and (13)C-MRS, which offer a broader chemical shift range and therefore can provide more detailed information at the level of single metabolites. The versatility of MRS allows for a wide range of clinical applications, of which neurodegeneration is an interesting target for spectroscopy-based studies. In particular, MRS can identify patterns of altered brain chemistry in Alzheimer's patients and can help establish differential diagnosis in Alzheimer's and Parkinson's diseases. Using MRS to follow less abundant neurotransmitters is currently out of reach and will most likely depend on the development of methods such as hyperpolarization that can increase the sensitivity of detection. In particular, dynamic nuclear polarization has opened up a new and exciting area of medical research, with developments that could greatly impact on the real-time monitoring of in vivo metabolic processes in the brain.

Nonmotor symptoms in Parkinson’s disease: the dark side of the moon

Nonmotor symptoms may appear during the course of Parkinson’s disease, complicating the advanced phase in particular, but are also common in the premotor phase of Parkinson’s disease. The appearance of nonmotor manifestations represents a milestone, determining a worse prognosis and lower quality of life; however, they are often misdiagnosed and untreated. The spectrum of nonmotor symptoms encompasses mood disorders, psychosis, dementia, sleep disorders, impulse-control disorders and autonomic dysfunctions. This article describes these nonmotor symptoms and their management.

Efficacy of rivastigmine on executive function in patients with Parkinson's disease dementia

BACKGROUND AND OBJECTIVE

Rivastigmine is approved in the USA for the treatment of mild to moderate Alzheimer's disease and Parkinson's disease dementia (PDD). Executive function (EF) deficits are a core symptom of PDD. The current objective was to investigate the effects of rivastigmine capsules versus placebo on EF in PDD, focusing on secondary outcome measures from a large, international, randomized, double-blind, placebo-controlled, 24-week trial (EXPRESS, CENA713B2311).

METHODS

Secondary outcomes included Delis-Kaplan Executive Function System (D-KEFS) measures of EF. Data from three D-KEFS subtests (Card Sorting, Letter Fluency, Color-Word Interference), plus the Symbol Digit Modalities Test were analyzed in the observed case (OC) population. Changes from baseline in the rivastigmine versus placebo groups were evaluated using the van Elteren test blocking for country.

RESULTS

Of 541 patients in the EXPRESS study, 402, 71, 97, and 65 patients provided data for Letter Fluency, Card Sorting and Color-Word Interference subtests, and the Symbol Digit Modalities Test, respectively. On Letter Fluency, rivastigmine was associated with improvements in correct responses, set loss errors, and responses made (all P < 0.05), but not repetition errors. Higher Card Sorting recognition description score (P= 0.03), and more correct substitutions on the Symbol Digit Modalities Test (P= 0.02) were also recorded.

CONCLUSION

Rivastigmine was associated with significant improvements over placebo on EF tests evaluating flexibility of thinking, problem solving and planning in patients with PDD. These findings support the hypothesis that rivastigmine may affect frontal subcortical circuits, which potentially contributes to observed clinical improvement associated with EF.

Comparing Cerebral White Matter Lesion Burdens between Parkinson's Disease with and without Dementia

Cerebral white matter lesions (CWMLs) have been suggested to be associated with an increased risk of dementia, disability, and death. CWMLs are more common in individuals with Alzheimer's disease (AD) than in normal elderly individuals of comparable age. Only a few studies have been done to determine whether CWMLs may influence cognitive decline in Parkinson's disease (PD). Fully developed PD with concurrent AD was reported to likely cause impaired cognition in spite of accumulating evidence suggesting that PD with dementia (PDD) is more closely associated with Lewy body (LB) pathology. Currently, contradictory data on the neuropathology of dementia in PD require further prospective clinicopathological studies in larger cohorts to elucidate the impact of AD and α-synuclein (SCNA) pathologies on the cognitive status in these disorders. Previous reports did not suggest CWMLs to be associated with an increased risk of PDD. After adjusting for age at death, age at onset of PD, and duration of PD, our recent study investigating CWMLs in PDD via autopsy has shown a positive correlation between the burden of CWMLs and PDD. The frequent co-existence of both LB and AD lesions suggests that both pathologies independently or synergistically contribute to both movement disorders and cognitive impairment. The individual and cumulative burden of CWMLs, LB lesions, and AD lesions may synergistically contribute to cognitive decline in LB disorders such as PDD.

Evaluation of dementia rating scales in Parkinson's disease dementia

Disease-specific assessments are not currently available for patients with Parkinson's disease dementia (PDD). This study evaluated the criterion-related validity and test-retest reliability of the Alzheimer's Disease Assessment scale cognitive subscale (ADAS-cog) in terms of sensitivity for differentiation between mild and moderate severity impairment in PDD. Six other dementia rating scales and cognitive tests were also examined. A total of 113 patients with PDD or Alzheimer disease were recruited into this 4-week, multicenter study, segregated into 2 severity groups based on Mini-Mental State Examination (MMSE) score. Mean ADAS-cog scores showed a statistically significant separation between mild and moderate severity patients in both dementias (P < .001). For the ADAS-cog, test-retest Spearman correlation coefficients were significant for each dementia type and severity. This study demonstrated the criterion-related validity and test-retest reliability for ADAS-cog in patients with PDD and strong correlations with MMSE. This supports the validity of previous results obtained with these measures in studies of patients with PDD.

BuChE-K and APOE epsilon4 allele frequencies in Lewy body dementias, and influence of genotype and hyperhomocysteinemia on cognitive decline

Apolipoprotein E (APOE) epsilon4 and butyrylcholinesterase-K (BuChE-K) are associated with an increased risk for Alzheimer's disease. The primary objective was to evaluate frequencies of these alleles in dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). A secondary objective was to evaluate influences on rate of cognitive decline. This analysis used data from participants consenting to pharmacogenetic testing in placebo-controlled rivastigmine studies. Allele frequencies in DLB and PDD were compared using logistic regression. Within the PDD placebo sample, associations with cognitive decline were evaluated (the DLB sample was too small for these evaluations). Fifty-seven DLB and 323 PDD subjects provided APOE and BuChE data. Allelic frequencies were higher in DLB, relative to PDD subjects, for BuChE-K (P = 0.06), APOE epsilon4 (P < 0.001), or both alleles together (P < 0.001). More rapid cognitive decline was seen in PDD patients carrying both alleles, compared with other genotypes. Subjects with hyperhomocysteinemia were associated with more rapid decline in the presence of BuChE-K, with or without APOE epsilon4. These results suggest that genetic and biochemical risk factors for AD and PDD pathology may be important in dementia onset and progression in these Lewy body disorders.

Emerging hypotheses regarding the influences of butyrylcholinesterase-K variant, APOE epsilon 4, and hyperhomocysteinemia in neurodegenerative dementias

Non-enzymatic functions of butyrylcholinesterase (BuChE) include prevention of the aggregation of amyloid-beta peptide (A beta) in a concentration-dependent manner. This is mediated by the C-terminus of the protein, distal from the enzymatic site. The BuChE-K variant polymorphism lowers expression of BuChE protein and/or alters C-terminal activity. In combination with factors that increase production or reduce elimination of A beta, and/or increase susceptibility to A beta toxicity - such as the apolipoprotein E (APOE) epsilon 4 allele and/or hyperhomocysteinemia - BuChE-K may accelerate cholinergic synaptic and neuronal damage and cognitive decline. A beta-mediated damage to ascending cholinergic pathways may be further accentuated by Lewy body and/or cerebrovascular disease. As the disease advances and functioning cholinergic synapses disappear, both the rapid cognitive decline and response to cholinesterase inhibitor therapy in individuals with these factors may diminish. Non-enzymatic functions of the BuChE protein, APOE epsilon 4 status and hyperhomocysteinemia influence the progression of pathology, symptom expression, and response to cholinesterase inhibition in a stage-specific manner in neurodegenerative disorders associated with Alzheimer, Lewy body and vascular pathology.

Access to special care dentistry, part 9. Special care dentistry services for older people

This article looks at three common neurological conditions associated with later years: stroke, Parkinson's disease and dementia. All of them impact on oral health, access to dental services and delivery of dental care, and treatment goals need to be adapted to take into account patients' changing needs, medical status, pattern of recovery or the stage of dementia that they have reached. The article concludes by considering the topic of elder abuse. The dental team may have a role both in identifying abuse and ensuring appropriate action is taken.

Diagnosis and management of Parkinson's disease dementia

Parkinson's disease (PD) has long been considered predominantly a motor disorder. However, its frequent association with dementia, which contributes significantly to the morbidity and mortality of the condition, is gaining increasing recognition. PD dementia (PDD) has a unique clinical profile and neuropathology, distinct from Alzheimer's disease (AD). Cholinergic deficits, a feature of both AD and PDD, underlie the rationale for cholinesterase inhibitor therapy in both conditions. In clinical practice, it is important that PDD should be recognised and appropriately treated. This review aims to outline the recently proposed clinical diagnostic criteria for PDD and to summarise the guidelines/recommendations published since 2006 on the use of cholinesterase inhibitors in the management of PDD. Although the cholinesterase inhibitor rivastigmine has recently been approved for the management of PDD, there remains a need for the development of novel therapies that can affect key mechanisms of the disease or prevent/delay patients with PD and mild cognitive impairment from progressing to PDD.

A critical reappraisal of current staging of Lewy-related pathology in human brain

Sporadic Parkinson disease (sPD) or brainstem-predominant type of Lewy body (LB) disease, and dementia with Lewy bodies (DLB), the two most frequent alpha-synucleinopathies, are progressive multisystem neurodegenerative disorders with widespread occurrence of alpha-synuclein (AS) deposits in the central, peripheral, and autonomic nervous system. For both LB-related disorders, staging/classification systems based on semiquantitative assessment of the distribution and progression pattern of Lewy-related/AS pathology are used that are considered to be linked to clinical dysfunctions. In PD, a six-stage system (Braak) has been suggested to indicate a predictable sequence of lesions with ascending progression from medullary and olfactory nuclei to the cortex, the first two presymptomatic stages being related to incidental LB disease, stages 3 and 4 with motor symptoms, and the last two (cortical) stages may be frequently associated with cognitive impairment. DLB, according to consensus pathologic guidelines, by semiquantitative scoring of AS pathology (LB density and distribution) in specific brain regions, is distinguished into three phenotypes (brainstem, transitional/limbic, and diffuse neocortical), also considering concomitant Alzheimer-related pathology. Retrospective clinico-pathologic studies, although largely confirming the staging system, particularly for younger onset PD with long duration, have shown that between 6.3 and 43% of the cases did not follow the proposed caudo-rostral progression pattern of AS pathology. There was sparing of medullary nuclei in 7-8.3% of clinically manifested PD cases with AS inclusions in midbrain and cortex corresponding to Braak stages 4 and 5, whereas mild parkinsonian symptoms were already observed in stages 2 and 3. There is considerable clinical and pathologic overlap between PD (with or without dementia) and DLB, corresponding to Braak LB stages 5 and 6, both frequently associated with variable Alzheimer-type pathology. Dementia often does not correlate with progressed stages of LB pathology, but may also be related to concomitant Alzheimer lesions or mixed pathologies. There is no relationship between Braak LB stage and the clinical severity of PD, and the predictive validity of this concept is doubtful, since large unselected, retrospective autopsy series in 30-55% of elderly subjects with widespread AS/Lewy-related pathology (Braak stages 5 and 6) reported no definite neuropsychiatric symptoms, suggesting considerable cerebral compensatory mechanisms. Applying the original criteria to large dementia samples, 49% of positive cases were not classifiable. Therefore, modified criteria for the categorization of Lewy-related pathology were proposed for patients with a history of dementia. The causes and molecular basis of the not infrequent deviations from the current staging schemes of AS pathology in PD and DLB, its relation to the onset of classical parkinsonian symptoms and for the lack of definite clinical deficits despite widespread AS pathology in the nervous system remain to be elucidated.