Reduced temporal lobe blood flow in Alzheimer's disease

The characteristics of cognitive and daily living functions of neurocognitive disorders with delusions in elderly Alzheimer's disease

Background

Delusions in neurocognitive disorder due to Alzheimer's disease (AD) worsen patients' cognitive functions and activities of daily living (ADL), increasing caregiver burden and the risk of mortality. AD patients with delusions tend to experience a more rapid decline in cognition and have demonstrated poorer performance on various cognitive function tests. Considering the prognosis of delusion in AD patients, it tends to be more favorable with appropriate treatment. However, there is a lack of neuropsychological research, specifically examining the impact of delusions in AD, characterized by progressive deterioration of cognitive function. This study investigates the impact of delusions on cognitive function and ADL under conditions controlling for disease severity.

Methods

We compared cognitive function and ADL in AD patients aged 65 years or older according to the presence of delusions. To assess longitudinal change, we analyzed data from patients monitored for an average of 15 to 16 months. We assessed cognitive function and ADL using the Seoul Neuropsychological Screening Battery-Second Edition (SNSB-II) and delusions using the Neuropsychiatric Inventory (NPI). We used IBM SPSS Statistics version 25.0 for all statistical analyses. The analysis was not adjusted for multiple comparisons. We investigated how delusions impact cognitive function and ADL, controlling for age, educational level, and disease severity.

Results

The delusions group exhibited poorer immediate recall of verbal memory than the non-delusions group. In the follow-up evaluation, patients who developed delusions had lower baseline cognitive function than those who did not, and their language fluency declined over time. In addition, we found the presence of delusions associated with worse functional impairment in ADL as the disease progressed.

Conclusion

While controlling for the severity of AD, we found no significant negative impacts of delusions on most cognitive functions. Nevertheless, it is noteworthy that the immediate recall of verbal memory and the Controlled Oral Word Association Test (COWAT)_animal sensitively detected the negative impact of delusions. Furthermore, since delusions are associated with worsening ADL, we understand that delusion treatment is important for improving the quality of life for patients and caregivers.

Changes in the choroid plexuses and brain barriers associated with high blood pressure and ageing

INTRODUCTION

The choroid plexuses, blood vessels, and brain barriers are closely related both in terms of morphology and function. Hypertension causes changes in cerebral blood flow and in small vessels and capillaries of the brain. This review studies the effects of high blood pressure (HBP) on the choroid plexuses and brain barriers.

DEVELOPMENT

The choroid plexuses (ChP) are structures located in the cerebral ventricles, and are highly conserved both phylogenetically and ontogenetically. The ChPs develop during embryogenesis, forming a functional barrier during the first weeks of gestation. They are composed of highly vascularised epithelial tissue covered by microvilli, and their main function is cerebrospinal fluid (CSF) production. The central nervous system (CNS) is protected by the blood-brain barrier (BBB) and the blood-CSF barrier (BCSFB). While the BBB is formed by endothelial cells of the microvasculature of the CNS, the BCSFB is formed by epithelial cells of the choroid plexuses. Chronic hypertension induces vascular remodelling. This prevents hyperperfusion at HBPs, but increases the risk of ischaemia at low blood pressures. In normotensive individuals, in contrast, cerebral circulation is self-regulated, blood flow remains constant, and the integrity of the BBB is preserved.

CONCLUSIONS

HBP induces changes in the choroid plexuses that affect the stroma, blood vessels, and CSF production. HBP also exacerbates age-related ChP dysfunction and causes alterations in the brain barriers, which are more marked in the BCSFB than in the BBB. Brain barrier damage may be determined by quantifying blood S-100β and TTRm levels.

Near-Lifespan Tracking of Cerebral Microvascular Degeneration in Aging to Alzheimer’s Continuum

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder affecting millions of people worldwide and is currently incurable. As the population ages, AD and related dementia are becoming the biggest epidemic in medical history: the number of people aged 65 and older with AD is projected to increase between two- and three-fold by 2050. Imaging and biomarker studies suggest that the pathophysiological processes of AD begin more than a decade before the diagnosis of dementia, opening the possibility of early, preemptive prediction. For accurate prediction, it is important although challenging to fully understand how multiple etiologies and age-related prodromal processes contribute to the onset of Alzheimer’s continuum, across a long period comparable to the lifespan. Addressing this challenge was one of the overarching transformative concepts at the 2015 AD Research Summit, “to develop new programs on systems biology and integrative physiology to gain a deeper understanding of the complex biology of the disease.”

Among other factors, cerebral microvascular degeneration (CMD) may play a key role in the onset and development of Alzheimer’s continuum, potentially prior to, along with, or independently of the beta-amyloid (Aβ) accumulation. Despite its importance for early detection and as a therapeutic target for early intervention, it is unknown whether CMD is a causal factor for AD pathogenesis or an early consequence of multifactorial conditions that lead to AD at a later stage. Here, this Viewpoint suggests that we should fill two critical knowledge gaps: (1) Temporal relationships between various CMDs and other key factors before/during/after the onset of Alzheimer’s continuum have not been established; (2) Little integrative study down to the capillary vessel level has been conducted on how individual defects in various microvascular structural and flow properties distinctly correlate with and/or contribute to neuronal degeneration. As the first step toward filling these gaps, I propose utilizing recent advances in microscopic imaging and image analysis techniques to longitudinally track a comprehensive set of CMDs over the lifespan in model animals, along with Aβ, tau, neuronal degeneration, and cognitive impairment when possible.

Slowed Temporal and Parietal Cerebrovascular Response in Patients with Alzheimer's Disease

BACKGROUND

Recent investigations now suggest that cerebrovascular reactivity (CVR) is impaired in Alzheimer's disease (AD) and may underpin part of the disease's neurovascular component. However, our understanding of the relationship between the magnitude of CVR, the speed of cerebrovascular response, and the progression of AD is still limited. This is especially true in patients with mild cognitive impairment (MCI), which is recognized as an intermediate stage between normal aging and dementia. The purpose of this study was to investigate AD and MCI patients by mapping repeatable and accurate measures of cerebrovascular function, namely the magnitude and speed of cerebrovascular response (τ) to a vasoactive stimulus in key predilection sites for vascular dysfunction in AD.

METHODS

Thirty-three subjects (age range: 52-83 years, 20 males) were prospectively recruited. CVR and τ were assessed using blood oxygen level-dependent MRI during a standardized carbon dioxide stimulus. Temporal and parietal cortical regions of interest (ROIs) were generated from anatomical images using the FreeSurfer image analysis suite.

RESULTS

Of 33 subjects recruited, 3 individuals were excluded, leaving 30 subjects for analysis, consisting of 6 individuals with early AD, 11 individuals with MCI, and 13 older healthy controls (HCs). τ was found to be significantly higher in the AD group compared to the HC group in both the temporal (p = 0.03) and parietal cortex (p = 0.01) following a one-way ANCOVA correcting for age and microangiopathy scoring and a Bonferroni post-hoc correction.

CONCLUSION

The study findings suggest that AD is associated with a slowing of the cerebrovascular response in the temporal and parietal cortices.

Acylated Ghrelin as a Multi-Targeted Therapy for Alzheimer's and Parkinson's Disease

Much thought has been given to the impact of Amyloid Beta, Tau and Alpha-Synuclein in the development of Alzheimer's disease (AD) and Parkinson's disease (PD), yet the clinical failures of the recent decades indicate that there are further pathological mechanisms at work. Indeed, besides amyloids, AD and PD are characterized by the culminative interplay of oxidative stress, mitochondrial dysfunction and hyperfission, defective autophagy and mitophagy, systemic inflammation, BBB and vascular damage, demyelination, cerebral insulin resistance, the loss of dopamine production in PD, impaired neurogenesis and, of course, widespread axonal, synaptic and neuronal degeneration that leads to cognitive and motor impediments. Interestingly, the acylated form of the hormone ghrelin has shown the potential to ameliorate the latter pathologic changes, although some studies indicate a few complications that need to be considered in the long-term administration of the hormone. As such, this review will illustrate the wide-ranging neuroprotective properties of acylated ghrelin and critically evaluate the hormone's therapeutic benefits for the treatment of AD and PD.

Genome-wide identification of novel long non-coding RNAs and their possible roles in hypoxic zebrafish brain

Long non-coding RNAs (lncRNAs) are the master regulators of numerous biological processes. Hypoxia causes oxidative stress with severe and detrimental effects on brain function and acts as a critical initiating factor in the pathogenesis of Alzheimer's disease (AD). From the RNA-Seq in the forebrain (Fb), midbrain (Mb), and hindbrain (Hb) regions of hypoxic and normoxic zebrafish, we identified novel lncRNAs, whose potential cis targets showed involvement in neuronal development and differentiation pathways. Under hypoxia, several lncRNAs and mRNAs were differentially expressed. Co-expression studies indicated that the Fb and Hb regions' potential lncRNA target genes were involved in the AD pathogenesis. In contrast, those in Mb (cry1b, per1a, cipca) was responsible for regulating circadian rhythm. We identified specific lncRNAs present in the syntenic regions between zebrafish and humans, possibly functionally conserved. We thus identified several conserved lncRNAs as the probable regulators of AD genes (adrb3b, cav1, stat3, bace2, apoeb, psen1, s100b).

Accelerated loss of hypoxia response in zebrafish with familial Alzheimer's disease-like mutation of presenilin 1

Ageing is the major risk factor for Alzheimer's disease (AD), a condition involving brain hypoxia. The majority of early-onset familial AD (EOfAD) cases involve dominant mutations in the gene PSEN1. PSEN1 null mutations do not cause EOfAD. We exploited putative hypomorphic and EOfAD-like mutations in the zebrafish psen1 gene to explore the effects of age and genotype on brain responses to acute hypoxia. Both mutations accelerate age-dependent changes in hypoxia-sensitive gene expression supporting that ageing is necessary, but insufficient, for AD occurrence. Curiously, the responses to acute hypoxia become inverted in extremely aged fish. This is associated with an apparent inability to upregulate glycolysis. Wild-type PSEN1 allele expression is reduced in post-mortem brains of human EOfAD mutation carriers (and extremely aged fish), possibly contributing to EOfAD pathogenesis. We also observed that age-dependent loss of HIF1 stabilization under hypoxia is a phenomenon conserved across vertebrate classes.

Vascular Dysfunction in Alzheimer's Disease: A Prelude to the Pathological Process or a Consequence of It?

Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.

Cerebral and Retinal Neurovascular Changes: A Biomarker for Alzheimer's Disease

Objectives

Biomarker quest for Alzheimer’s disease (AD) has gone a long way by studying various anatomical, physiological and biochemical parameters for detecting disease onset and predicting prognosis. Almost all the studies converge on the single hypothesis of the amyloid and Tau pathway. Recently, vascular hypothesis has evolved drawing attention towards a complex dynamic anatomical and physiological entity, neuro-vascular (NV) unit. Pathological changes at this level, altering the normal physiology such as auto-regulation and dynamics of blood brain barrier have been hypothesized as a probable basis for AD. This paper attempts to review the existing data on the vascular hypothesis and the current trends in analyzing the NV unit in AD.

Design

This review initially focuses on the cerebral NV coupling followed by the retinal neurovascular coupling that mirrors the cerebral pathophysiology. The pathophysiology and the potential tools to diagnose AD at the level of NV unit are analyzed. Further, it examines the drawbacks in existing methods for analyzing the same.

Findings

None of the current studies have emphasized the importance of studying the complex dynamic NV unit as a whole. This review strongly recommends the combination of vascular and neuro-glial parameters using objective methods for estimating the physiological and pathological changes in the NV unit.

Discussion and conclusion

This review highlights the importance of retina for non-invasive estimation of the same. Also, novel algorithms for retinal image analysis have been proposed. The purpose of this review is to highlight the importance of retinal findings in neurodegenerative disorders and to create awareness among the neuroophthalmologists, of the potential benefits of ophthalmological tools in screening dementia patients.

Choroid plexus dysfunction impairs beta-amyloid clearance in a triple transgenic mouse model of Alzheimer's disease

Compromised secretory function of choroid plexus (CP) and defective cerebrospinal fluid (CSF) production, along with accumulation of beta-amyloid (Aβ) peptides at the blood-CSF barrier (BCSFB), contribute to complications of Alzheimer’s disease (AD). The AD triple transgenic mouse model (3xTg-AD) at 16 month-old mimics critical hallmarks of the human disease: β-amyloid (Aβ) plaques and neurofibrillary tangles (NFT) with a temporal- and regional- specific profile. Currently, little is known about transport and metabolic responses by CP to the disrupted homeostasis of CNS Aβ in AD. This study analyzed the effects of highly-expressed AD-linked human transgenes (APP, PS1 and tau) on lateral ventricle CP function. Confocal imaging and immunohistochemistry revealed an increase only of Aβ42 isoform in epithelial cytosol and in stroma surrounding choroidal capillaries; this buildup may reflect insufficient clearance transport from CSF to blood. Still, there was increased expression, presumably compensatory, of the choroidal Aβ transporters: the low density lipoprotein receptor-related protein 1 (LRP1) and the receptor for advanced glycation end product (RAGE). A thickening of the epithelial basal membrane and greater collagen-IV deposition occurred around capillaries in CP, probably curtailing solute exchanges. Moreover, there was attenuated expression of epithelial aquaporin-1 and transthyretin (TTR) protein compared to Non-Tg mice. Collectively these findings indicate CP dysfunction hypothetically linked to increasing Aβ burden resulting in less efficient ion transport, concurrently with reduced production of CSF (less sink action on brain Aβ) and diminished secretion of TTR (less neuroprotection against cortical Aβ toxicity). The putative effects of a disabled CP-CSF system on CNS functions are discussed in the context of AD.

Initial mini-mental state and cerebral perfusion in Alzheimer's disease

PURPOSE

The relationship between the initial mini-mental state examination (MMSE) score and cerebral perfusion was evaluated in patients with Alzheimer's disease (AD).

METHODS

In the study single photon emission computed tomography (SPECT) images of the brains of 40 AD patients were compared with the brain scans of 10 healthy controls. Each patient underwent MMSE analysis at initial evaluation as well as Tc-99 m hexamethylpropyleneamine oxine (HMPAO) brain SPECT. The patients were followed up for at least 42 months.

RESULTS

The regional cerebral blood flow (rCBF) values for patients were found to be significantly decreased for all cerebral lobes compared to the control subjects and p-values were calculated to be less than 0.001 except for occipital lobes. The most statistically significant correlation between the MMSE scores and rCBF values was determined for the left temporal lobe (p < 0.0001). A significant correlation was also found for the right temporal lobe (p < 0.005). A minimal statistically significant correlation was found for the frontal lobes and the left parietal lobe (p < 0.05).

CONCLUSIONS

The overall cerebral perfusion was decreased except in the occipital lobes in AD cases with low initial MMSE scores and there was a significant relationship between the decrease in perfusion of the temporal/frontal lobes and the left parietal lobe with the decrease in the initial MMSE scores. The most significant relationship between the decrease in the initial MMSE scores and the rCBF values was determined for the temporal lobes (especially for the left temporal lobe). It was also found that the left frontal lobe was affected from the beginning of the disease.

Assessment of activation of the plasma kallikrein-kinin system in frontal and temporal cortex in Alzheimer's disease and vascular dementia

Decreased cerebral blood flow and blood-brain barrier disruption are features of Alzheimer's disease (AD). The plasma kallikrein-kinin system modulates cerebrovascular tone through release of vasoactive bradykinin (BK). Cerebroventricular infusion of Aβ1-40 enhances BK release, suggesting that the activity of this system may be elevated in AD. We investigated the profile of the activating protease of this system, plasma kallikrein (PK), in frontal and temporal brain tissue from postmortem confirmed cases of AD, vascular dementia (VaD), and controls. Measurements of neuron specific enolase messenger ribonucleic acid (mRNA) and protein were used to adjust for neuronal loss. Adjusted PK mRNA was significantly increased in the frontal cortex in AD, and the frontal and temporal cortex in VaD. Similar trends were seen for PK protein level in AD and VaD. PK activity was significantly increased in the frontal and temporal cortex in AD. Increased PK activity in AD is likely to contribute to increased BK release and may thereby influence cerebral blood flow and vascular permeability.

Biomarkers for prediction and targeted prevention of Alzheimer's and Parkinson's diseases: evaluation of drug clinical efficacy

Neurodegenerative diseases like Parkinson’s disease (PD) and Alzheimer’s disease (AD) are considered disorders of multifactorial origin, inevitably progressive and having a long preclinical period. Therefore, the availability of biological markers or biomarkers (BMs) for early disease diagnosis will impact the management of AD and PD in several dimensions; it will 1) help to capture high-risk individuals before symptoms develop, a stage where prevention efforts might be expected to have their greatest impact; 2) provide a measure of disease progression that can be evaluated objectively, while clinical measures are much less accurate; 3) help to discriminate between true AD or PD and other causes of a similar clinical syndrome; 4) delineate pathophysiological processes responsible for the disease; 5) determine the clinical efficacy of novel, disease-modifying (neuroprotective) strategies. In the long run the availability of reliable BMs will significantly advance the research and therapeutics of AD and PD.

Biomarkers for evaluation of clinical efficacy of multipotential neuroprotective drugs for Alzheimer's and Parkinson's diseases

During the last century, the world population has shown a staggering increase in its proportion of elderly members and thus neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD), respectively, are becoming an increasing burden on society. Among the diverse, significant challenges facing clinicians, is the improvement of diagnostic measures to detect early and subtle symptoms, a phase in which prevention efforts might be expected to have their greatest impact and provide a measure of disease progression that can be evaluated during the course of drug treatment. At present, clinical diagnosis of AD and PD is based on a constellation of symptoms and manifestations, although the disease originated several years earlier. Given the multiple etiological nature of AD and PD, it is reasonable to assume that the initial causative pathobiological processes may differ between the affected individuals. Therefore, the availability of biological markers or biomarkers will help not only early disease diagnosis, but also delineate the pathological mechanisms more definitively and reliably than the traditional cognitive and neurological phenotypes. In the current article, we review the literature on biochemical, genetic, and neuroimaging biomarkers and discuss their predictive value as indicative for disease vulnerability to detect individuals at risk for PD and AD, and to determine the clinical efficacy of novel, disease-modifying (neuroprotective) strategies.

Microvascular injury and blood-brain barrier leakage in Alzheimer's disease

Thinning and discontinuities within the vascular basement membrane (VBM) are associated with leakage of the plasma protein prothrombin across the blood-brain barrier (BBB) in Alzheimer's disease (AD). Prothrombin immunohistochemistry and ELISA assays were performed on prefrontal cortex. In severe AD, prothrombin was localized within the wall and neuropil surrounding microvessels. Factor VIII staining in severe AD patients indicated that prothrombin leakage was associated with shrinkage of endothelial cells. ELISA revealed elevated prothrombin levels in prefrontal cortex AD cases that increased with the Braak stage (Control=1.39, I-II=1.76, III-IV=2.28, and V-VI=3.11 ng prothrombin/mg total protein). Comparing these four groups, there was a significant difference between control and Braak V-VI (p=0.0095) and also between Braak stages I-II and V-VI (p=0.0048). There was no significant difference in mean prothrombin levels when cases with versus without cerebral amyloid angiopathy (CAA) were compared (p-value=0.3627). When comparing AD patients by APOE genotype (ApoE3,3=2.00, ApoE3,4=2.49, and ApoE4,4=2.96 ng prothrombin/mg total protein) an analysis of variance indicated a difference between genotypes at the 10% significance level (p=0.0705). Tukey's test indicated a difference between the 3,3 and 4,4 groups (p=0.0607). These studies provide evidence that in advanced AD (Braak stage V-VI), plasma proteins like prothrombin can be found within the microvessel wall and surrounding neuropil, and that leakage of the blood-brain barrier may be more common in patients with at least one APOE4 allele.

Molecular neuroimaging in Alzheimer's disease

Considerable data exist to support the use of positron emission tomography (PET) and single photon emission computed tomography (SPECT) scanning as biomarkers for Alzheimer's disease (AD). The techniques are reasonably sensitive and specific in differentiating AD from normal aging, and recent studies with pathological confirmation show good sensitivity and specificity in differentiating AD from other dementias. These techniques also can detect abnormalities in groups of asymptomatic and presymptomatic individuals and may be able to predict decline to dementia. However, there are a number of existing questions related to the use of these techniques in samples that are fully representative of the spectrum of patients with dementia. For example, it is unclear how well PET and SPECT perform in comparison to a clinical diagnosis obtained in the same patient group, when autopsy is used as a gold standard. It will also be important to know what PET and SPECT add to the certainty of diagnosis in addition to the standard clinical diagnosis. Despite these unanswered questions, PET and SPECT may have application as biomarkers for AD in a number of clinical and research settings, especially in academic centers, where most of the existing studies have been done.

Volume reduction in cerebral blood flow in patients with Alzheimer's disease: a sonographic study

Neuroimaging techniques such as PET and SPECT demonstrated a consistent reduction of cerebral blood flow (CBF) in Alzheimer's disease (AD). The aim of the study was to assess the potential role of ultrasonography for CBF measurement in AD patients and whether the CBF volume correlates positively with disease severity. Fifty patients who met the diagnostic criteria of probable AD (NINDS-ADRDA) were compared to 50 age-matched healthy elderly volunteers. The extracranial internal carotid arteries (ICAs) and the vertebral arteries (VAs) of the patients and controls were examined. Angle-corrected time-averaged flow velocity (TAV) and the diameter of the vessel were measured. Intravascular flow volumes were calculated as the product of TAV and the cross-sectional area of the circular vessel. CBF volume was calculated as the sum of flow volumes in the ICAs and VAs of both sides. All subjects underwent the MMSE. The mean global CBF (474.87 +/- 94.085 vs. 744.26 +/- 94.082 ml/min; p < 0.0001) was lower in AD patients than in healthy volunteers. A significant decline in global flow volumes (r = 0.48; p < 0.0007) with the degree of cognitive impairment was also present. The ability of ultrasonography to characterize flow decreases makes such a technique an attractive tool for the study of AD, for the evaluation of pharmacological therapies and, possibly, for early diagnosis.

Biological correlates of clinical subgroups of Alzheimer's disease

We considered it possible that the differences in clinical symptoms between two suggested subgroups of Alzheimer's disease (AD), AD type I and AD type II, have biological correlates, for instance different metabolic profiles. Therefore, we performed regional cerebral blood flow (rCBF) measurements and investigated the cerebrospinal fluid (CSF) levels of the monoamine metabolites homovanillic acid (HVA), 5-HIAA, and HMPG in 15 patients with AD type I, in 36 patients with AD type II, in a control group and in a contrast group consisting of 16 patients with frontotemporal dementia. The results suggest that there are underlying biological correlates of the phenomenological discrepancies between AD type I and AD type II. For instance, a decreased CSF level of HVA (p < 0.001) was specific to AD type I and decreased rCBF (p < 0.05 to <0.001) in three particular regions was specific to AD type II.

Relationship between blood flow kinetics and severity of Alzheimer's disease: assessment of severity using a questionnaire-type examination, Alzheimer's disease assessment scale, cognitive sub-scale (ADAS(cog))

We assessed hemokinetics associated with changes in Alzheimer's disease (AD) severity in 90 AD patients by researching the relationship between AD Assessment Scale, cognitive sub-scale (ADAS(cog)) scores and regional cerebral blood flow (rCBF). In the present study, we employed the questionnaire-type ADAS(cog) examination to accurately assess the severity of AD. Between five groups classified on the basis of ADAS(cog) score, significant differences were observed in parietal, lateral temporal and superior frontal rCBF. In addition, in parietal and lateral temporal regions, significant correlations were also observed between ADAS(cog) score and rCBF. In superior frontal rCBF, significant differences were noted only between group 5 (> or =40 ADAS(cog) points) and each of the other groups; there was no significant correlation between rCBF and ADAS(cog) score. Thus, we propose the following mechanism for blood flow kinetics associated with changed severity: In an early stage of AD, blood flow in the medial temporal cortex is impaired, and gradually involves the temporoparietal regions. While the medial temporal impairment of blood flow reaches a plateau, temporoparietal blood flow continues to be impaired well into a severe stage, at which point blood flow impairment in the frontal region is initiated.

Cerebral microvascular pathology in aging and Alzheimer's disease

The aging of the central nervous system and the development of incapacitating neurological diseases like Alzheimer's disease (AD) are generally associated with a wide range of histological and pathophysiological changes eventually leading to a compromised cognitive status. Although the diverse triggers of the neurodegenerative processes and their interactions are still the topic of extensive debate, the possible contribution of cerebrovascular deficiencies has been vigorously promoted in recent years. Various forms of cerebrovascular insufficiency such as reduced blood supply to the brain or disrupted microvascular integrity in cortical regions may occupy an initiating or intermediate position in the chain of events ending with cognitive failure. When, for example, vasoconstriction takes over a dominating role in the cerebral vessels, the perfusion rate of the brain can considerably decrease causing directly or through structural vascular damage a drop in cerebral glucose utilization. Consequently, cerebral metabolism can suffer a setback leading to neuronal damage and a concomitant suboptimal cognitive capacity. The present review focuses on the microvascular aspects of neurodegenerative processes in aging and AD with special attention to cerebral blood flow, neural metabolic changes and the abnormalities in microvascular ultrastructure. In this context, a few of the specific triggers leading to the prominent cerebrovascular pathology, as well as the potential neurological outcome of the compromised cerebral microvascular system are also going to be touched upon to a certain extent, without aiming at total comprehensiveness. Finally, a set of animal models are going to be presented that are frequently used to uncover the functional relationship between cerebrovascular factors and the damage to neural networks.

Donepezil dose-dependently inhibits acetylcholinesterase activity in various areas and in the presynaptic cholinergic and the postsynaptic cholinoceptive enzyme-positive structures in the human and rat brain

In the symptomatic treatment of mild to moderately severe dementia associated with Alzheimer's disease, donepezil (E2020) has been introduced for the inhibition of acetylcholinesterase activity in the human brain. However, there is no morphological evidence as to how this chemical agent affects the acetylcholinesterase-positive structures in the various areas of the human and the rat CNS. This study demonstrates by histochemical means that donepezil exerts a dose-dependent inhibitory effect in vitro on acetylcholinesterase activity. The most sensitive areas were the cortex and the hippocampal formation. Within the different layers of the cortex, the cholinoceptive acetylcholinesterase-positive postsynaptic pyramidal cell bodies were more sensitive than the presynaptic cholinergic axonal processes. In the cortex, the cell body staining was already abolished by even 2 x 10(-8)M donepezil, whereas the axonal staining could be eliminated only by at least 5 x 10(-8)M donepezil. In the hippocampus, the axonal acetylcholinesterase reaction end-product was eliminated by 5 x 10(-7)M donepezil. The most resistant region was the putamen, where the staining intensity was moderately reduced by 1 x 10(-6)M donepezil. In the rat brain, the postsynaptic cholinoceptive and presynaptic cholinergic structures were inhibited by nearly the same dose of donepezil as in the human brain. These histochemical results provide the first morphological evidence that, under in vitro circumstances, donepezil is not a general acetylcholinesterase inhibitor in the CNS, but rather selectively affects the different brain areas and, within these, the cholinoceptive and cholinergic structures. The acetylcholinesterase staining in the nerve fibers (innervating the intracerebral blood vessels of the human brain and the extracerebral blood vessels of the rat brain) and at the neuromuscular junction in the diaphragm and gastrocnemius muscle of rat, was also inhibited dose dependently by donepezil. It is concluded that donepezil may be a valuable tool with which to influence both the pre- and the postsynaptic acetylcholinesterase-positive structures in the human and rat central and peripheral nervous systems.

The role of estrogen replacement therapy in Alzheimer's disease

Multiple factors appear to contribute to the expression of Alzheimer's disease (AD). About 30% of cases of dementia of the Alzheimer's type (DAT) can be attributed to genetic factors. These observations raise the possibility of identifying multiple interventions that may modify the disease process and, therefore, the clinical expression of the dementia. Prominent among factors that may contribute to dementia and, specifically, to dementia of the Alzheimer's type is cerebral vascular disease. Estrogen is a potent factor that not only prevents vascular disease but also improves blood flow in diseased vessels, including blood flow in regions of the brain affected by AD. Estrogen also has direct effects on neuronal function that may play an important role not only in the preservation of neurons but in the repair of neurons damaged by the disease process. These effects of estrogen on the CNS suggest that the hormone may be effective not only in the prevention of dementia but also in its treatment. Given the distressingly high prevalence of AD among older women and the exorbitant social and economic costs associated with this disorder, a true risk reduction on the order of one-third to one-half, as suggested by several recent analytical studies, would be of tremendous public health importance.

Neuroimaging in dementia

Positron emission tomography, single photon emission computed tomography, and MR imaging are brain imaging techniques that have been applied widely to the study of patients with dementia. This article reviews current data on the clinical use of these techniques in the differential diagnosis of dementia and the prediction of dementia in those at risk.

Frontotemporal dementia can be distinguished from Alzheimer's disease and subcortical white matter dementia by an anterior-to-posterior rCBF-SPET ratio

Sixteen patients with frontotemporal dementia (FTD), 27 with early-onset Alzheimer's disease, 25 with late-onset Alzheimer's disease, 19 with subcortical white matter dementia (SWD) and 28 normal controls underwent semiquantitative regional cerebral blood flow measurement (rCBF) using single-photon emission tomography (SPET; (99m)Tc-HMPAO) and either computerized tomography (CT) or magnetic resonance imaging (MRI) of the brain. An anterior-to-posterior rCBF-SPET ratio (mesial superior frontal gyrus/medial temporal lobes) was calculated, which significantly separated the FTD group from the other dementia groups and controls with a sensitivity of 87.5% and a specificity of at least 78.6%. CT/MRI was found to be helpful in the differential diagnosis between FTD and SWD. In FTD patients, the mesial superior frontal gyrus, near the polus frontalis, was found to be the region with the most reduced rCBF values.

Similar ultrastructural breakdown of cerebrocortical capillaries in Alzheimer's disease, Parkinson's disease, and experimental hypertension. What is the functional link?

The brain, as an intensely active organ, is highly dependent on a sufficient nutrient and oxygen availability in order to reach its optimal working capacity. It is well known that the vital supply of energy substrates is provided by the circulatory system, which splits up into a fine, terminal capillary network in target tissues. These capillaries are considered as important sites, since the actual nutrient trafficking takes place through their walls. That is why an intact, preserved structure of the microvessels is crucial to fulfill their function. Since the brain is known to be particularly vulnerable to suboptimal oxygen and glucose delivery, the intact morphology of capillaries is of paramount importance. Several observations have indicated that the cerebral capillary ultrastructure is damaged in Alzheimer's disease (AD). Curiously, the regional cerebral blood flow of AD patients is also significantly lower than in age-matched control individuals. Based on these data, it has been suggested that the decreased blood supply and the cerebrovascular alterations contribute to the development of dementia. However, we have observed similar capillary damage in Parkinson's disease patients and chronically hypertensive rats in addition to AD cases, as presented here. These findings indicate that cerebral capillary damage is not exclusive for AD but occurs under other neurodegenerative disorders and hypertension, as well. We hypothesize that ultrastructural abnormalities of cerebral capillaries are causally related to decreased cerebral blood flow and create a condition that favors neurodegenerative mechanisms including the development of dementia.

Are Alzheimer's disease, hypertension, and cerebrocapillary damage related?

Alzheimer's disease (AD) patients are often subject to vascular dysfunction besides their specific CNS pathology, which warrants further examination of the interaction between vascular factors and the development of dementia. The association of decreased cerebral blood flow (CBF) or hypertension with AD has been a target of growing interest. Parallel with physiological changes, the cerebral capillaries in AD are also prone to degenerative processes. The microvascular abnormalities that are the result of such degeneration may be the morphological correlates of the vascular pathophysiology pointing to a compromised nutrient transport through the capillaries. Animal models have been developed to study the consequences of hypertension and reduced CBF. Spontaneously hypertensive rats are widely used in hypertension research whereas ligation of the carotid arteries has become a method to produce cerebral hypoperfusion. Based on these models, we propose a relationship between hypertension, cerebral hypoperfusion, cerebral capillary malformation and cognitive decline as it occurs in AD. We suggest that the above conditions are functionally related and can contribute to the progression of AD.

Nursing documentation versus standardized assessment of cognitive status in hospitalized medical patients

Although the literature discusses the importance of assessing cognitive status, little research has explored the concordance of nurses' documentation of cognitive status and standardized assessment. This study examined nurses documentation of cognitive status in 42 medically hospitalized individuals (mean age 51.9, SD = 10.1 years) using a variety of standardized measures. Although the chart review revealed no documentation of impaired cognitive status, impaired performance in 24 to 67% of the cognitive measures was identified. This study suggests nurses are missing cognitive impairment in hospitalized patients by limiting assessment to orientation. Use of a combination of several brief screening measures, such as the Clock Drawing Test and the standardized Mini-Mental State Examination, would provide timely, effective, and inexpensive assessment of cognitive status.

Alzheimer disease: protective factors

Approximately 6-8% of all persons aged >65 y have Alzheimer disease and the prevalence of the disease is increasing. Any intervention strategy aimed at decreasing risks or delaying the onset of the disease will therefore have a substantial effect on health care costs. Nutrition seems to be one of the factors that may play a protective role in Alzheimer disease. Many studies suggest that oxidative stress and the accumulation of free radicals are involved in the pathophysiology of the disease. Several studies have shown the existence of a correlation between cognitive skills and the serum concentrations of folate, vitamin B-12, vitamin B-6, and, more recently, homocysteine. However, nutritional factors have to be studied not alone but with the other factors related to Alzheimer disease: genetics, estrogen, antiinflammatory drug use, and socioeconomic variables. The objective of this article was to review recent studies in this field.

Use of estrogens for the prevention and treatment of Alzheimer's disease

This review examines the biological rationale for the use of estrogen replacement therapy (ERT) and the evidence for the efficacy of ERT in enhancing cognition, preventing Alzheimer's disease (AD) and treating AD in postmenopausal women. While the biological basis for ERT as a cognition enhancer is strong and multiply mediated, the clinical evidence for its use is not as compelling and must be weighed against possible side effects. Until the results of definitive large trials are available, the use of ERT alone or in combination with other treatments is worthy of consideration.

Preserved benzodiazepine receptors in Alzheimer's disease measured with C-11 flumazenil PET and I-123 iomazenil SPECT in comparison with CBF

This study evaluates the regional cerebral blood flow (CBF) with H2(15)O-PET and the distribution of central benzodiazepine receptor (BZR) with C-11 flumazenil (FMZ) by PET and I-123 iomazenil (IMZ) by SPECT in Alzheimer's disease (AD). In AD, whereas the CBF was diminished in the frontal, temporal, parietal, and occipital cortex, the distribution volume of FMZ and delayed activity of IMZ were relatively preserved in these cortices, suggesting that the BZR reduction, reflecting neuronal loss, is less prominent than the CBF suppression. The mini-mental state examination score (MMS) was weakly correlated with the CBF in the parietal cortex but not with BZR. It is speculated that the neuronal density reflected by BZR is less impaired than the neuronal function assessed with blood flow in the association cortex of AD. High correlation was found between the uptake of FMZ and the delayed activity of IMZ. The delayed image of IMZ-SPECT is clinically useful to evaluate the preservation of neuronal density in the affected temoporoparietal association cortex in AD.

Selective excitation of subtypes of neocortical interneurons by nicotinic receptors

The cellular mechanisms by which neuronal nicotinic cholinergic receptors influence many aspects of physiology and pathology in the neocortex remain primarily unknown. Whole-cell recordings and single-cell reverse transcription (RT)-PCR were combined to analyze the effect of nicotinic receptor agonists on different types of neurons in acute slices of rat neocortex. Nicotinic receptor agonists had no effect on pyramidal neurons and on most types of interneurons, including parvalbumin-expressing fast spiking interneurons and somatostatin-expressing interneurons, but selectively excited a subpopulation of interneurons coexpressing the neuropeptides vasoactive intestinal peptide (VIP) and cholecystokinin. This excitation persisted in the presence of glutamate, GABA, and muscarinic receptor antagonists and in the presence of tetrodotoxin and low extracellular calcium, suggesting that the depolarization was mediated through the direct activation of postsynaptic nicotinic receptors. The responses were blocked by the nicotinic receptor antagonists dihydro-beta-erythroidine and mecamylamine and persisted in the presence of the alpha7 selective nicotinic receptor antagonist methyllycaconitine, suggesting that the involved nicotinic receptors lacked the alpha7 subunit. Single-cell RT-PCR analysis indicated that the majority of the interneurons that responded to nicotinic stimulation coexpressed the alpha4, alpha5, and beta2 nicotinic receptor subunits. Therefore, these results provide a role for non-alpha7 nicotinic receptors in the selective excitation of a subpopulation of neocortical interneurons. Because the neocortical interneurons expressing VIP have been proposed previously to regulate regional cortical blood flow and metabolism, these results also provide a cellular basis for the neuronal regulation of cortical blood flow mediated by acetylcholine.

Cerebral hypoperfusion yields capillary damage in the hippocampal CA1 area that correlates with spatial memory impairment

The impact of chronic cerebral hypoperfusion on cognitive function and cerebral capillary morphology in the hippocampus was examined. Young adult Wistar rats were subjected to permanent ligation of both common carotid arteries (two-vessel occlusion). One month after vascular occlusion, a small but non-significant impairment in the acquisition of spatial information was registered compared with sham-operated controls. Two months after surgery, the occluded animals displayed an impaired performance throughout the training period. One year after surgery, the acquisition curves demonstrated a significant attenuation of the learning rate in the occluded rats group, whereas no significant differences in long-term retention were observed. Thus, chronic hypoperfusion induced by two-vessel occlusion gave rise to impairment of spatial memory. Following behavioural testing, the rats were killed at the age of 17 months, and capillaries in the CA1 and dentate gyrus were examined using transmission electron microscopy. Typical age-related capillary abnormalities such as degenerative pericytes and thickened basement membranes (with or without fibrosis) were detected in the hippocampus of sham animals. In occluded rats, the occurrence of capillaries displaying such abnormalities almost doubled in the CA1 region, but was similar in the dentate gyrus, compared with sham controls. A highly significant correlation was found between the last Morris maze performance and the percentage of capillaries with deposits in the basement membrane in the hippocampal CA1 area of occluded rats, which was not present in the sham animals. We conclude that a long-term hypoperfusion accelerated the development of age-related ultrastructural aberrations of capillaries in the hippocampal CA1 area, but not in the dentate gyrus. Thus, not only neurons, but also capillaries in the hippocampal CA1 area are sensitive to an impaired microcirculation. Moreover, the cognitive performance of hypoperfused rats correlated closely with the condition of the capillaries in the CA1 area, suggesting that capillary integrity is one of the important determinants of brain function in conditions that compromise cerebral microcirculation.

Re-evaluating the role of vascular changes in the differential diagnosis of Alzheimer's disease and vascular dementia

Alzheimer's disease (AD) and vascular dementia (VaD) are the two most common causes of dementia, and much effort has been devoted to their differential diagnosis. However, current epidemiological, clinical and neuropathological evidence points to a substantial overlap between AD and VaD and suggests that vascular pathology, the traditional cornerstone of the differential diagnosis between the two entities, may not represent as clear a line of demarcation as originally believed. It may be time to reevaluate the dichotomy between AD and VaD.

Longitudinal SPECT study in Alzheimer's disease: relation to apolipoprotein E polymorphism

OBJECTIVES

In mild Alzheimer's disease, SPECT imaging of regional cerebral blood flow has highlighted deficits in the posterior association cortex, and later in the disease process, the deficit spreads to involve the frontal cortex. The sigma4 allele of apolipoprotein E is a risk factor for Alzheimer's disease. The effect of apolipoprotein E polymorphism on cerebral perfusion was studied. The hypothesis was that those patients with Alzheimer's disease who carry the sigma4 allele would have more severe cerebral hypoperfusion.

METHODS

Thirty one patients with Alzheimer's disease and eight age and sex matched control subjects were examined in a three year longitudinal study. Patients with Alzheimer's disease were divided into subgroups according to their number of sigma4 alleles. Regional cerebral blood flow ratios referred to the cerebellum were examined by 99mTc-HMPAO SPECT. Apolipoprotein E genotypes were determined by digestion of polymerase chain reaction products with the restriction enzyme Hha1.

RESULTS

All patients with Alzheimer's disease had bilateral temporoparietal hypoperfusion compared with control subjects. The two sigma4 allele subgroups had the lowest ratios at the baseline assessment in the parietal and occipital cortices, and at the follow up in the temporal, parietal, and occipital cortices. They had the highest reduction in percentage terms in the temporal and occipital cortices compared with the other subgroups. However, the global clinical severity did not differ at the baseline or follow up examinations between the subgroups.

CONCLUSION

Apolipoprotein E polymorphism is involved in the pathogenesis and heterogeneity of Alzheimer's disease as the most severe cerebral hypoperfusion was found in the sigma4 allele subgroups. This might have implications for therapeutic approaches in Alzheimer's disease.

Alzheimer's disease risk factors as related to cerebral blood flow: additional evidence

In a previous report, Alzheimer's disease risk factors, including alcohol abuse, depression, Down's syndrome, cerebral glucose metabolism defect, head trauma, old age, Parkinson's disease, sleep disturbance, and underactivity, were shown to have an association with reduced cerebral blood flow. In this report an attempt is made to strengthen a hypothesis that reduced cerebral blood flow may be a required cofactor in the cause of Alzheimer's disease with examples of additional putative risks, including aluminum, ApoE 4 alleles, estrogen deficiency, family history of dementia, low education-attainment, olfactory deficit, and underactivity coupled with gender, considered to have a relationship or potential relationship with reduced cerebral blood flow. Factors, believed to ameliorate Alzheimer's disease, associated with improved or stabilized cerebral blood flow are tabulated. A tentative cerebral blood flow nomogram is shown as a potential model to possibly help predict Alzheimer's disease susceptibility.

Can neuroimaging techniques identify individuals at risk of developing Alzheimer's disease?

Recent studies indicate that neuroimaging techniques such as magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography can accurately differentiate patients with Alzheimer's disease (AD) from elderly controls. This report reviews the results of neuroimaging studies of two at-risk populations: subjects with the epsilon 4 allele of the apolipoprotein E and those with mild cognitive impairment. The results of the work published to date indicate that the presence of the epsilon 4 allele is a risk factor for AD and that its predictive validity can be enhanced by neuropsychological and/or neuroimaging evaluation. The results also show that patients with mild cognitive impairment display a number of structural and functional imaging abnormalities that are more pronounced in the temporal and parietal lobes. We suggest that the use of neuroimaging techniques can improve the detection of subjects early in the course of AD, although the sensitivity and the specificity of this approach still await a more detailed prospective evaluation.

Cerebral vessels in ageing and Alzheimer's disease

The integrity of the cerebral vasculature is crucial to the maintenance of cognitive functions during ageing. Prevailing evidence suggests that cerebrovascular functions decline during normal ageing, with pronounced effects in Alzheimer's disease (AD). The causes of these changes largely remain unknown. While previous studies recorded ageing-related impairments, such as atherosclerosis and loss of innervation in basal surface arteries of the brain, it only recently has been realized that a number of subtle alterations in both the intracranial resistance vessels and the smaller capillaries is apparent in both ageing animals and humans. The dominant changes include alterations in composition of connective tissues and smooth muscle of large vessel walls, thickening of the vascular basement membrane, thinning of the endothelium in some species, loss of endothelial mitochondria and increased pericytes. Some of these attributes appear more affected in AD. Other abnormalities entail profound irregularities in the course of microvessels, unexplained inclusions in the basement membrane and changes in unique proteins and membrane lipids associated with the blood-brain barrier. Brain imaging and permeability studies show no clear functional evidence to support the structural and biochemical anomalies, but it is plausible that focal and transient breach of the blood-brain barrier in ageing, and more notably in AD, occurs. Thus, circumscribed neuronal populations in certain brain regions could become vulnerable. Furthermore, the characteristic deposition of amyloid in vessels in AD may exacerbate the decline in vascular function and promote chronic hypoperfusion. Although not explicit from current studies, it is likely that the brain vasculature is continually modified by growth and repair mechanisms in attempts to maintain perfusion during ageing and disease.

Clinical studies of cerebral blood flow in Alzheimer's disease

Studies of Alzheimer's disease using single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have found reductions in blood flow and glucose metabolism in temporal and parietal cortex. In 50 AD patients who underwent neuropsychological testing and SPECT perfusion imaging, we found significant correlations between perfusion and performance on the Mini-Mental Status Examination in the frontal and parietal lobes. In addition, specific correlations between perfusion in the frontal lobes and performance on tests of frontal lobe ability were noted. These findings, while suggesting the importance of perfusion measures in determining clinical features of the disease, do not clearly define perfusion changes as primary, since similar findings have been seen when metabolism is studied. In a separate group of 5 AD patients and 16 controls, we used PET with the perfusion tracer HIPDM and examined cerebrovascular reactivity to carbon dioxide inhalation. We found that in multiple brain regions, including the temporal lobes, AD patients showed robust and significant increases in perfusion in response to carbon dioxide that did not differ from the response seen in the controls. Taken together, these results show that while perfusion changes are important in AD, they are not clearly either primary or limiting.

Constraints on the cerebral basis for semantic processing from neuroimaging studies of Alzheimer's disease

OBJECTIVE

Functional activation studies of semantic processing in healthy adults have yielded conflicting results. The purpose was to evaluate the relative role of the brain regions implicated in semantic processing with converging evidence from imaging studies of patients with impaired semantic processing.

METHODS

Semantic memory was assessed in patients with Alzheimer's disease using two measures, and these performance patterns were related to profiles of reduced cerebral functioning obtained with high resolution single photon emission computed tomography (SPECT). Patients with frontotemporal degeneration were similarly evaluated as a control group.

RESULTS

Reduced relative cerebral perfusion was seen in parietal and posterior temporal brain regions of patients with Alzheimer's disease but not patients with frontotemporal degeneration. Impairments on semantically guided category membership decision tasks were also seen in patients with Alzheimer's disease but not those with frontotemporal degeneration. Performance on the semantic measures correlated with relative cerebral perfusion in inferior parietal and superior temporal regions of the left hemisphere only in Alzheimer's disease. Relative perfusion was significantly lower in these regions in patients with Alzheimer's disease with semantic difficulty compared with patients with Alzheimer's disease with relatively preserved semantic processing.

CONCLUSION

These findings provide converging evidence to support the contribution of superior temporal and inferior parietal regions of the left hemisphere to semantic processing.

The ratio of mesial to neocortical temporal lobe blood flow as a predictor of dementia

OBJECTIVE

The hypothesis tested was that an increased ratio of cerebral blood flow (rCBF) in the mesocortical temporal lobe to that of the neocortical temporal lobe (MES/ NEO ratio) would be related to clinical measures of dementia severity and would help distinguish Alzheimer's patients from normal controls.

DESIGN

The rCBF of nine Alzheimer's patients (5 males and 4 females; age = 65.9 +/- 6.0 years, range 55-71; Folstein Mini-Mental Status Examination = 18.6 +/- 7.4, range 9-28) and 10 age-matched normal controls (7 males, 3 females; age = 66.0 +/- 5.7 years, range 58-75) was determined by positron emission tomography (PET) using H2(15)0 and the method of Alpert et al.

RESULTS

Alzheimer's disease patients had a significantly higher MES/NEO ratio (1.19 +/- .17) than the age-matched normal controls (.854 +/- .14; t = .-4.74, df = 17, P = .0002). Using a MES/NEO ratio of 1 as the cutoff point for discrimination between Alzheimer's patients and normal controls, the ratio demonstrated 100% sensitivity (no. of correctly identified Alzheimer's patients/no. of Alzheimer's patients) and 90% specificity (no. of correctly identified unaffected subjects/no. of unaffected subjects). Further, those patients with the highest MES/NEO ratios had the lowest overall measures of cognitive function (Folstein Mini-Mental Status Examination: r = -.75, P < .02, 1-tail; Mattis Dementia Rating Scale: r = -0.655, P = .028, 1-tail) scores.

CONCLUSIONS

The findings are consistent with other in vivo and postmortem studies, suggesting that functional and structural changes of the lateral temporal lobe in Alzheimer's disease occur relatively early in the disease process and appear to be distinguishable from those changes accompanying normal aging. In contrast, the memory loss and pathology of the mesial temporal lobe that is characteristic of the early stages of Alzheimer's patients do not appear to be associated with a reduction in cerebral blood flow in the resting Alzheimer's patient. Nevertheless, the clinical significance of the results must await findings of longitudinal studies of larger numbers of Alzheimer's patients and controls.

Regional HmPAO SPECT and CT measurements in the diagnosis of Alzheimer's disease

BACKGROUND

This study investigated the hypothesis that the combination of regional CT brain atrophy measurements and semiquantitative SPECT regional blood flow ratios could produce a diagnostic test for Alzheimer's disease (AD) with an accuracy comparable to that achieved with the present clinical gold standard of the NINCDS-ADRDA criteria.

METHODS

Single proton emission computed tomography (SPECT) and CT head scans were performed on 122 subjects referred an UBC Alzheimer clinic and diagnosed as either 'not demented' (ND-37) or 'possible/probable AD' (AD-85) by the NINCDS-ADRDA criteria. Stepwise discriminant analysis (SDA) was performed on the bilateral SPECT regions of interest and compared to bilateral CT qualitative/quantitative assessment in the frontal, parietal and temporal lobes to determine which were most accurate at ND/AD distinction. Receiver operating curves (ROC) were then constructed for these variables individually and for their combined discriminant function.

RESULTS

The left temporal qualitative cortical atrophy score (CT) and left temporal perfusion ratio (SPECT) were selected in the SDA. The combined discriminant function was more specific at AD/ND distinction than either of CT or SPECT alone. The accuracy of AD/ND distinction with the combined discriminant function was below that achieved by clinical diagnosis according to the NINCDS-ADRDA criteria and was not significantly different from that achieved with SPECT or CT alone as defined by ROC curve analysis.

CONCLUSION

The measurements of left temporal cortical atrophy and regional cerebral blood flow were most indicative of AD; however they lacked the sensitivity and specificity to recommend their use as a diagnostic test for AD.

Regional cerebral blood volume measured by dynamic susceptibility contrast MR imaging in Alzheimer's disease: a principal components analysis

Dynamic susceptibility contrast (DSC) MRI is an alternative to positron emission tomography (PET) and single photon emission computed tomography (SPECT) for the evaluation of cerebral hemodynamics in patients with Alzheimer's disease. DSC MRI allows the construction of high resolution images of cerebral blood volume (CBV) without the use of radionuclides or ionizing radiation. In this study, DSC MRI data were collected from 16 patients with probable Alzheimer's disease and 16 age-matched control subjects. Characteristic patterns of regional CBV variation were found using principal component analysis. Three such patterns were identified: a global variation pattern, an anterior-to-posterior CBV gradient, and a temporoparietal pattern. Group differences in the principal component scores associated with the global and temporoparietal patterns (P = .08 and P = .007, respectively) suggest that these deficits reflect characteristic CBV abnormalities in Alzheimer's disease. Using only these two scores, the Alzheimer's disease group was classified with a sensitivity of 81% and a specificity of 88%. Additionally, disease severity, as measured by the Mini-Mental State Examination (MMSE), was correlated significantly with the third principal component score (Pearson's r = .50, P = .05).

Sensitivity, specificity, and positive predictive value of technetium 99-HMPAO SPECT in discriminating Alzheimer's disease from other dementias

Investigators have reported high sensitivity and specificity values for single photon emission computerized tomography (SPECT) when distinguishing Alzheimer's disease (AD) patients from normal elderly controls or from selected patient groups. The role of SPECT in identifying AD among unselected patients with memory complaints requires investigation. We examined 139 consecutive patients with 99Tc-HMPAO SPECT. NINCDS-ADRDA diagnoses were determined blind to SPECT results, and scans were read and classified by visual inspection blind to clinical diagnoses. Bilateral temporoparietal hypoperfusion (TP) occurred in 75% of probable, 65% of possible, and 45% of unlikely AD patients, yielding a sensitivity of 75% and a specificity of 52% when comparing probable AD versus unlikely AD groups. A positive predictive value of 78% was obtained based on a 69% prevalence of AD in our total clinic population. Patients with false-positive results included a variety of dementing illnesses; all patients with bilateral hypoperfusion had dementia. A pattern of TP on SPECT scans is seen in most patients with AD, but could be found in other dementias as well and cannot be regarded as specific to AD. Reduced TP perfusion discriminated between demented and nondemented individuals. Further strategies for SPECT interpretation that improve diagnostic specificity should be sought.