Clinical history, brain metabolism, and neuropsychological function in Alzheimer's disease

Aiming for [18F]FDG-PET acquisition time reduction in clinical practice for neurological patients

PURPOSE

Positron emission tomography (PET) imaging with [18F]FDG provides valuable information regarding the underlying pathological processes in neurodegenerative disorders. PET imaging for these populations should be as short as possible to limit head movements and improve comfort. This study aimed to validate an optimized [18F]FDG-PET image reconstruction protocol aiming to reduce acquisition time while maintaining adequate quantification accuracy and image quality.

METHODS

A time-reduced reconstruction protocol (5 min) was evaluated in [18F]FDG-PET retrospective data from healthy individuals and Alzheimer's disease (AD) patients. Standard (8 min) and time-reduced protocols were compared by means of image quality and quantification accuracy metrics, as well as standardized uptake value ratio (SUVR) and Z-scores (pons was used as reference). Images were randomly and blindly presented to experienced physicians and scored in terms of image quality.

RESULTS

No differences between protocols were identified during the visual assessment. Small differences (p < 0.01) in the pons SUVR were observed between the standard and time-reduced protocols for healthy individuals (-0.002 ± 0.011) and AD patients (-0.007 ± 0.013). Likewise, incorporating the PSF correction in the reconstruction algorithm resulted in small differences (p < 0.01) in SUVR between protocols (healthy individuals: -0.003 ± 0.011; AD patients: -0.007 ± 0.014).

CONCLUSION

Quality metrics were similar between time-reduced and standard protocols. In the visual assessment of the images, the physicians did not consider the use of PSF adequate, as it degraded the quality image. Shortening the acquisition time is possible by optimizing the image reconstruction parameters while maintaining adequate quantification accuracy and image quality.

Chronic Social Defeat Stress Modulates Dendritic Spines Structural Plasticity in Adult Mouse Frontal Association Cortex

Chronic stress is associated with occurrence of many mental disorders. Previous studies have shown that dendrites and spines of pyramidal neurons of the prefrontal cortex undergo drastic reorganization following chronic stress experience. So the prefrontal cortex is believed to play a key role in response of neural system to chronic stress. However, how stress induces dynamic structural changes in neural circuit of prefrontal cortex remains unknown. In the present study, we examined the effects of chronic social defeat stress on dendritic spine structural plasticity in the mouse frontal association (FrA) cortex in vivo using two-photon microscopy. We found that chronic stress altered spine dynamics in FrA and increased the connectivity in FrA neural circuits. We also found that the changes in spine dynamics in FrA are correlated with the deficit of sucrose preference in defeated mice. Our findings suggest that chronic stress experience leads to adaptive change in neural circuits that may be important for encoding stress experience related memory and anhedonia.

Alzheimer's disease: clinical, neuropathologic, neuropsychologic, and brain metabolic findings

Approximately four million individuals over 65 years ofage sufferfrom some form of dementia. A majority of these people sufferfrom an Alzheimer's-type dementia. Brain alterations associated with this disease process include neurofibrillary tangles and senile plaques and reductions in concentrations of chemical messengers. Alzheimer's-type dementia is typified by a slow decline in intellect andpersonality. It is usually diagnosed after other possibilities have been excluded, and can be correctly diagnosed only upon autopsy. Over 12 of these chemical messenger systems have been examined in Alzheimer's disease. Brain tissue of autopsied Alzheimer's patients has revealed reductions in chemical messenger systems such as the cholinergic, noradrenergic, dopaminergic, serotoninergic, and recently, somatostatin and corticotropin. Treatment strategies based on the deficits of these chemical systems has been unremarkable to date. The only treatment that has yielded positive results thus far has been with a drug of the cholinergic system, physostigmine. However, side effects limit its use. A new brain scanning methodology called Positron Emission Tomography has revealed brain metabolic deficits in the parietal and temporal lobes of the brain in patients with mild to moderate Alzheimer's disease. Patients with severe Alzheimer's disease have brain metabolic deficits throughout their brain. Effective study ofAlzheimer's disease must encompass clinicalandpost-mortem studies that include brain chemical evaluations in addition to PET scanning. A combined approach willyield a better understanding of what Alzheimer's-type dementia is, how it progresses, and how it might better be treated.

CNS Assessment Using Functional Neuro-PET Imaging

Disorders of the brain manifest in a variety of manners ranging from feeling or thought abnormalities to total paralysis. Until recently, most imaging methods of the brain have been limited to anatomic considerations, with little information about actual function of the brain except that deduced from clinical examination and physical and cognitive assessment testing. With the advent of positron emission tomography (PET) and enhanced computer and scintigraphic image detection systems, there is keen interest in applying this imaging technique to better understand brain physiology and pathophysiology. Potential applications of PET in CNS assessment is expanding avenues for improved diagnosis and staging of disease, as well as monitoring therapeutic interventions. A general review of the radiopharmaceuticals used for neuro-PET imaging, as well as their application in situations such as cerebrovascular disease, brain activation studies, various movement disorders and dementias, depression, epilepsy, obsessive-compulsive disorder, schizophrenia, and neuropharmacology (including cerebral receptor studies) will be presented.

Frontal association cortex is engaged in stimulus integration during associative learning

The frontal association cortex (FrA) is implicated in higher brain function. Aberrant FrA activity is likely to be involved in dementia pathology. However, the functional circuits both within the FrA and with other regions are unclear. A recent study showed that inactivation of the FrA impairs memory consolidation of an auditory fear conditioning in young mice. In addition, dendritic spine remodeling of FrA neurons is sensitive to paired sensory stimuli that produce associative memory. These findings suggest that the FrA is engaged in neural processes critical to associative learning. Here we characterize stimulus integration in the mouse FrA during associative learning. We experimentally separated contextual fear conditioning into context exposure and shock, and found that memory formation requires protein synthesis associated with both context exposure and shock in the FrA. Both context exposure and shock trigger Arc, an activity-dependent immediate-early gene, expression in the FrA, and a subset of FrA neurons was dually activated by both stimuli. In addition, we found that the FrA receives projections from the perirhinal (PRh) and insular (IC) cortices and basolateral amygdala (BLA), which are implicated in context and shock encoding. PRh and IC neurons projecting to the FrA were activated by context exposure and shock, respectively. Arc expression in the FrA associated with context exposure and shock depended on PRh activity and both IC and BLA activities, respectively. These findings indicate that the FrA is engaged in stimulus integration and contributes to memory formation in associative learning.

Activity of P-Glycoprotein, a β-Amyloid Transporter at the Blood-Brain Barrier, Is Compromised in Patients with Mild Alzheimer Disease

Studies in animals and postmortem human brain tissue support a role for P-glycoprotein in clearance of cerebral β-amyloid across the blood-brain barrier (BBB). We tested the hypothesis that BBB P-glycoprotein activity is diminished in Alzheimer disease (AD) by accounting for an AD-related reduction in regional cerebral blood flow (rCBF).

METHODS

We compared P-glycoprotein activity in mild-AD patients (n = 9) and cognitively normal, age-matched controls (n = 9) using PET with a labeled P-glycoprotein substrate, (11)C-verapamil, and (15)O-water to measure rCBF. BBB P-glycoprotein activity was expressed as the (11)C-verapamil radioactivity extraction ratio ((11)C-verapamil brain distributional clearance, K1/rCBF).

RESULTS

Compared with controls, BBB P-glycoprotein activity was significantly lower in the parietotemporal, frontal, and posterior cingulate cortices and hippocampus of mild AD subjects.

CONCLUSION

BBB P-glycoprotein activity in brain regions affected by AD is reduced and is independent of rCBF. This study improves on prior work by eliminating the confounding effect that reduced rCBF has on assessment of BBB P-glycoprotein activity and suggests that impaired P-glycoprotein activity may contribute to cerebral β-amyloid accumulation in AD. P-glycoprotein induction or activation to increase cerebral β-amyloid clearance could constitute a novel preventive or therapeutic strategy for AD.

Progressive Nonfluent Aphasia: Language, Cognitive, and PET Measures Contrasted with Probable Alzheimer's Disease

The purpose of this study was to compare the language and cognitive profiles of four progressive nonfluent aphasia (PNFA) patients with 25 probable Alzheimer's disease (pAD) patients, and to identify the distinct cortical defects associated with cognitive deficits in PNFA using positron emission tomography (PET). Longitudinal observations of PNFA patients revealed progressively telegraphic speech and writing and a gradual deterioration of sentence comprehension, but memory and visual functioning were relatively preserved. Direct contrast with PAD patients revealed that PNFA patients are significantly impaired on grammatical phrase structure aspects of sentence comprehension and expression, phonemic judgments, repetition, and digit span, but not on other cognitive measures. PET studies of PNFA revealed reduced cortical activity throughout the left hemisphere. In addition, there was a prominent defect in left superior and middle temporal and inferior frontal regions of PNFA patients that differed significantly from the distribution of regional cerebral dysfunction in pAD. We conclude that PNFA is associated with a distinct profile of language and cognitive difficulty, and that this pattern of impairment is related to cortical dysfunction in a specific distribution of the left hemisphere.

Brain fuel metabolism, aging, and Alzheimer's disease

Lower brain glucose metabolism is present before the onset of clinically measurable cognitive decline in two groups of people at risk of Alzheimer's disease--carriers of apolipoprotein E4, and in those with a maternal family history of AD. Supported by emerging evidence from in vitro and animal studies, these reports suggest that brain hypometabolism may precede and therefore contribute to the neuropathologic cascade leading to cognitive decline in AD. The reason brain hypometabolism develops is unclear but may include defects in brain glucose transport, disrupted glycolysis, and/or impaired mitochondrial function. Methodologic issues presently preclude knowing with certainty whether or not aging in the absence of cognitive impairment is necessarily associated with lower brain glucose metabolism. Nevertheless, aging appears to increase the risk of deteriorating systemic control of glucose utilization, which, in turn, may increase the risk of declining brain glucose uptake, at least in some brain regions. A contributing role of deteriorating glucose availability to or metabolism by the brain in AD does not exclude the opposite effect, i.e., that neurodegenerative processes in AD further decrease brain glucose metabolism because of reduced synaptic functionality and hence reduced energy needs, thereby completing a vicious cycle. Strategies to reduce the risk of AD by breaking this cycle should aim to (1) improve insulin sensitivity by improving systemic glucose utilization, or (2) bypass deteriorating brain glucose metabolism using approaches that safely induce mild, sustainable ketonemia.

Imaging biomarkers and their role in dementia clinical trials

There are five potential major roles for neuroimaging with respect to dementia; (1) as a cognitive neuroscience research tool, (2) for prediction of which normal or slightly impaired individuals will develop dementia and over what time frame, (3) for early diagnosis of Alzheimer's disease (AD) in demented individuals, (sensitivity) and separation of AD from other forms of dementia (specificity), (4) for monitoring of disease progression, and (5) for monitoring response to therapies. Focusing on the last role, no single imaging approach is yet ideal, as all trade-off speed, cost, and accuracy. Functional imaging (SPECT and PET) is best suited to tracking symptomatic therapy response, and anatomic (MRI volumetric) imaging or amyloid PET are more suited to reflect dementia modulation studies. The potential for imaging with respect to pharmacological studies of dementia--to provide surrogate markers for drug studies, to improve diagnosis, to speed evaluation of outcomes, and to decrease sample sizes--is huge. At the present time, however, no single measure has sufficient proven reliability, replicability, or robustness, to replace clinical primary outcome measures.

Comparative proteomic analysis using samples obtained with laser microdissection and saturation dye labelling

Comparative proteomic methods are rapidly being applied to many different biological systems including complex tissues. One pitfall of these methods is that in some cases, such as oncology and neuroscience, tissue complexity requires isolation of specific cell types and sample is limited. Laser microdissection (LMD) is commonly used for obtaining such samples for proteomic studies. We have combined LMD with sensitive thiol-reactive saturation dye labelling of protein samples and 2-D DIGE to identify protein changes in a test system, the isolated CA1 pyramidal neurone layer of a transgenic (Tg) rat carrying a human amyloid precursor protein transgene. Saturation dye labelling proved to be extremely sensitive with a spot map of over 5,000 proteins being readily produced from 5 mug total protein, with over 100 proteins being significantly altered at p < 0.0005. Of the proteins identified, all showed coherent changes associated with transgene expression. It was, however, difficult to identify significantly different proteins using PMF and MALDI-TOF on gels containing less than 500 mug total protein. The use of saturation dye labelling of limiting samples will therefore require the use of highly sensitive MS techniques to identify the significantly altered proteins isolated using methods such as LMD.

[18F]FDG-PET in patients with Alzheimer's disease: marker of disease spread

BACKGROUND

It is not known yet whether temporoparietal glucose hypometabolism in patients with probable Alzheimer's disease (AD) reflects disease severity or different subtypes of patients.

METHODS

Twenty-five subjects with mild probable AD [NINCDS-ADRDA criteria; age 65.8 +/- 9.3 years (mean +/- SD); Mini-Mental State Examination (MMSE) 26.0 +/- 3.3] were investigated. [(18)F]FDG-PET data were analyzed visually with raters blinded to the diagnosis and with a quantitative analysis in the region of interest on individual anatomically normalized PET scans.

RESULTS

Thirteen of 25 patients showed temporoparietal hypometabolism on visual inspection (PET+; age 65.7 +/- 10.7), 12 patients had normal FDG-PET results (PET-; age 65.9 +/- 8.0; n.s.). The MMSE and immediate reproduction of the Wechsler Memory Scale (WMS-R-I) were 27.7 +/- 1.9 and 31.1 +/- 6.1 in the PET- vs. 24.5 +/- 3.6 (p = 0.012) and 22.0 +/- 7.4 (p = 0.006) in the PET+ group. Immediate and delayed recall in the California Verbal Learning Test and delayed reproduction in the Wechsler Memory Scale were alike. Regression analysis revealed a significant correlation of temporoparietal glucose metabolism with the block span (r = 0.60; p < 0.01) and the WMS-R-I (r = 0.68; p < 0.01) but not with measures of hippocampal function.

CONCLUSIONS

Temporoparietal glucose metabolism in patients with very mild AD is a sign of disease spread beyond the temporal lobe. This may aid in establishing objective parameters for future therapeutic studies.

The role of PET imaging in the management of patients with central nervous system disorders

PET will continue to play a critical role in both clinical and research applications with regard to CNS disorders. PET is useful in the initial diagnosis of patients presenting with CNS symptoms and can help clinicians determine the best course of therapy. PET studies can also be useful for studying the response to therapy. From the research perspective, the various neurotransmitter and other molecular tracers currently available or in development will provide substantial information about pathophysiologic process in the brain. As such applications become more widely tested, their introduction into the clinical arena will further advance the use of PET imaging in the evaluation and management of CNS disorders.

Age and ApoE genotype interaction in Alzheimer's disease: an FDG-PET study

Previous positron emission tomography (PET) studies with fluorodeoxglucose (FDG) as tracer in healthy elders showed that the epsilon4 allele of the apolipoprotein E (ApoE) gene is disruptive to cerebral glucose metabolism (rCMRglu), possibly through the interaction with the aging process. The present study was aimed at assessing whether this interaction occurs in patients with Alzheimer's disease (AD). Eight-six AD patients, including 40 ApoE4 carriers and 46 non-carriers, underwent (18)F-FDG PET scanning at rest. ApoE groups were comparable for age, gender, age at onset and disease duration. SPM'99 was used to assess rCMRGlu correlations with age, differences between ApoE groups and ApoE by age interaction, correcting for disease severity. Results were reported at P<0.001, uncorrected. Correlations between age and rCMRGlu confirmed the well-known negative relationship for both groups. Lower rCMRGlu was found within the frontal and cingulate areas for ApoE4 carriers as compared with the non-carriers. Additionally, a significant ApoE by age interaction was detected in the frontal and anterior cingulate cortex, with the ApoE4 carriers having a steeper regression slope with respect to the non-carriers. These results indicate that age-related regional rCMRglu decreases within the frontal and anterior cingulate areas may be more severe in AD patients carrying the ApoE4 allele.

Limbic hypometabolism in Alzheimer's disease and mild cognitive impairment

The neural basis of the amnesia characterizing early Alzheimer's disease (AD) remains uncertain. Postmortem pathological studies have suggested early involvement of the mesial temporal lobe, whereas in vivo metabolic studies have shown hypometabolism of the posterior cingulate cortex. Using a technique that combined the anatomic precision of magnetic resonance imaging with positron emission tomography, we found severe reductions of metabolism throughout a network of limbic structures (the hippocampal complex, medial thalamus, mamillary bodies, and posterior cingulate) in patients with mild AD. We then studied a cohort with mild cognitive impairment in whom amnesia was the only cognitive abnormality and found comparable hypometabolism through the same network. The AD and mild cognitive impairment groups were differentiated, however, by changes outside this network, the former showing significant hypometabolism in amygdala and temporoparietal and frontal association cortex, whereas the latter did not. The amnesia of very early AD reflects severe but localized limbic dysfunction.

Brain glucose hypometabolism after perirhinal lesions in baboons: implications for Alzheimer disease and aging

The authors previously reported that excitotoxic lesions of both the perirhinal and entorhinal cortices in baboons induce remote neocortical and hippocampal hypometabolism reminiscent of that observed in Alzheimer disease (AD), suggesting that disconnection may play a role in AD. Because the cerebral metabolic rate of glucose (CMR ) was preferentially correlated with perirhinal damage, the area first affected by neurofibrillary tangles in both AD and normal aging, the present series of experiments aimed at assessing the specific metabolic effects of perirhinal lesions. Using PET, CMR was measured before surgery and sequentially over the ensuing 10 months. Compared with sham-operated baboons, perirhinal lesions induced significant-albeit late and transient-CMR decreases in several brain regions, which significantly correlated with histologic damage for some of these regions. Among them, the temporal and hippocampal regions are metabolically affected after extensive rhinal lesions, in early AD, and aging, while the prefrontal region is affected in aging only. Furthermore, in contrast to AD and rhinal lesions, the posterior cingulate cortex was spared. Both the progressive but significant metabolic effects and specific hypometabolic pattern after perirhinal lesions were confirmed by direct comparisons with previous data obtained after combined lesions of both rhinal areas. Thus, although perirhinal damage appears in itself insufficient to induce sustained CMR decreases, it may contribute to the hypometabolic profile of both AD and normal aging, most likely with a stronger contribution in the latter.

A cost analysis of positron emission tomography

OBJECTIVE

Changes in regulations and improvements in reimbursement have propelled positron emission tomography (PET) into clinical use, making it increasingly important to understand the costs of this emerging service. Cost analyses are important tools to do this. Data published previously on these topics reflect assumptions that are no longer valid. The aim of this study was to determine the cost of developing and operating a PET facility and to evaluate whether a regional cyclotron serving several scanners reduces costs.

MATERIALS AND METHODS

Financial data were collected on capital expense and global operating costs through interviews with industry experts, evaluation of prior studies, and review of expenses incurred at the University of Southern California PET center. A data model and cost templates were developed. Expenses were allocated either to the production or purchase of radiopharmaceuticals or to the provision of the PET scan, and the cost per procedure was determined. A sensitivity analysis was performed on the net present value for key parameters.

RESULTS

A cyclotron serving a single scanner is not financially viable. The radiopharmaceutical distribution configurations were financially sound. In these cases, the cost of the radiopharmaceutical was approximately $700 per dose with modest levels of production (12 doses per day). In addition, the average cost of PET scans (technical scan and professional charges) ranged from approximately $900 to $1400. The critical factor for profitability was shown to be throughput.

CONCLUSION

This analysis provides significant insight into the cost of PET and the comparative costs of offering PET through four operating configurations. Reductions in equipment prices, increased availability of radiopharmaceuticals, growth in demand, and improvements in reimbursement have all contributed to the financial viability of this imaging technique.

Cerebral blood flow and metabolic abnormalities in Alzheimer's disease

In this review I summarize observations of PET and SPECT studies about cerebral blood flow and metabolic abnormalities in Alzheimer's disease. In very early AD flow or metabolism reduces first in the posterior cingulate gyrus and precuneus. This reduction may arise from functional deafferentation caused by primary neural degeneration in the remote area of the entorhinal cortex that is the first to be pathologically affected in AD. Then medial temporal structures and parietotemporal association cortex show flow or metabolic reduction as disease processes. The reason why flow or metabolism in medial temporal structures shows delay in starting to reduce in spite of the earliest pathological affection remains to be elucidated. It is likely that anterior cingulate gyrus is functionally involved, since attention is the first non-memory domain to be affected, before deficits in language and visuospatial functions. However few reports have described involvement in the anterior cingulate gyrus. Relationship between cerebral blood flow or metabolism and apolipoprotein E genotype has been investigated. Especially, the APOE epsilon4 allele has been reported to increase risk and to lower onset age as a function of the inherited dose of the epsilon4 allele. Reduction of flow or metabolism in the posterior cingulate gyrus and precuneus has been reported even in presymptomatic nondemented subjects who were cognitively normal and had at least a single epsilon4 allele. On the contrary the relation of epsilon4 allele to the progression rate of AD has been controversial from neuroimaging approaches. PET and SPECT imaging has become to be quite useful for assessing therapeutical effects of newly introduced treatment for AD. Recent investigations observed significant regional flow increase after donepezil hydrochloride treatment. Most of these observations have been made by applying computer assisted analysis of three-dimensional stereotactic surface projection or statistical parametric mapping instead of a conventional regions of interest technique.

Histamine H(1) receptors in patients with Alzheimer's disease assessed by positron emission tomography

Cerebral histamine H(1) receptor binding was measured in vivo in 11 normal subjects (six young and five old) and 10 patients with Alzheimer's disease by positron emission tomography and [11C]doxepin, a radioligand for H(1) receptors. The parametric images describing the tracer kinetics were generated by either compartmental or graphical analysis, and were examined statistically on region-of-interest and voxel-by-voxel bases. The binding potential of H(1) receptors showed a significant decrease particularly in the frontal and temporal areas of the Alzheimer's disease brain compared to the old, normal subjects. In addition, the receptor binding correlated closely to the severity of Alzheimer's disease assessed by the Mini-Mental State Examination score within several brain areas. The ratio of K1 values between the brain areas and the cerebellum was used as a relative measure of regional cerebral blood flow which decreased in the frontal and temporal areas of the Alzheimer's disease brain. However, the difference in the binding potential (total concentration of receptor/equilibrium dissociation constant) between the Alzheimer's disease patients and the old, normal subjects was greater than that in the cerebral blood flow, and the rate of decrease in the binding potential with the progression of Alzheimer's disease was greater than the rate of decrease in the cerebral blood flow. This study reveals the predominant disruption of the histaminergic neurotransmission in the neurodegenerative processes of Alzheimer's disease. This study suggests that the decline of the histamine receptor binding might play a substantial role in the cognitive deficits of Alzheimer's disease patients.

Voxel-based analysis of confounding effects of age and dementia severity on cerebral metabolism in Alzheimer's disease

Alzheimer's disease is characterized by early hippocampal lesions, but neuropathological and functional imaging studies have also demonstrated involvement of associative cortices in patients suffering from this illness. New image-processing technologies have led to demonstration of predominant posteromedial cortical metabolic impairment in the disease. Confounding effects of both age and dementia severity on brain metabolism were assessed using categorical and correlational analyses performed with Statistical Parametric Mapping. Posterior cingulate and precuneus metabolism, assessed by positron emission tomography, was significantly correlated with age in a population of 46 patients with probable Alzheimer's disease. Metabolism in posterior cingulate and precuneus was higher in elderly than in younger patients with a diagnosis of Alzheimer's disease, even when dementia severity was taken as a confounding covariate. The data suggest that the sensitivity of positron emission tomography for the diagnosis of Alzheimer's disease is reduced in elderly cases, where less severe pathology is sufficient to induce clinical symptoms of dementia. Conversely, higher posteromedial metabolic impairment in early onset cases may reflect greater density of regional cerebral lesions or major decrease of functional afferences in a richly connected multimodal associative area. Posterior cingulate metabolism was also correlated to dementia severity, even when age was taken as a confounding covariate, whereas metabolism in the hippocampal formation was not shown to correlate with global cognitive deficit. Functional correlation was maintained between posterior cingulate and middle frontal cortex in demented patients as in elderly controls. The key role of posteromedial cortex in cognitive dysfunction assessed in Alzheimer's disease is probably related to its highly integrated position within attentional, visuospatial and memory neuronal networks.

Evaluation of standardized uptake value to assess cerebral glucose metabolism

PURPOSE

When the cerebral metabolic rate of glucose (CMRglc) is to be measured, arterial blood sampling is usually required for fluorine-18 fluorodeoxyglucose (FDG) and positron emission tomography (PET) studies. However, blood sampling is inconvenient because it requires several staff members and is invasive for patients.

METHODS

To assess cerebral glucose metabolism by a noninvasive and simplified method, the authors used the standardized uptake value (SUV), which requires no input function or blood sampling. The study participants included 18 healthy volunteers (4 men and 14 women; mean +/- SD age, 68.2+/-6.3 years), 18 patients with mild Alzheimer's disease (AD) (4 men and 14 women; mean +/- SD age, 68.8+/-7.3 years), and 18 patients with moderate AD (5 men and 13 women, mean +/- SD age, 69.5+/-8.5 years). Regional CMRglc and regional cerebral SUV were measured in the three groups using FDG PET, and the correlation between global CMRglc and global SUV was estimated.

RESULTS

The correlation coefficients of global CMRglc and global SUV in the healthy volunteers, mild AD patients, and moderate AD patients were 0.82, 0.67, and 0.62, respectively. Compared with the healthy persons, the patients with mild AD showed significantly decreased CMRglc in the temporal, frontal, and parietal cortices, but they did not show significantly decreased SUV in any region. Patients with moderate AD had significantly decreased CMRglc in the temporal, frontal, occipital, parietal, and sensorimotor cortices and significantly decreased SUV in the temporal, frontal, occipital, and parietal cortices.

CONCLUSION

The SUV would be useful as a semiquantitative index of cerebral glucose metabolism only in healthy persons or those with mild AD.

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.

Neocortical and hippocampal glucose hypometabolism following neurotoxic lesions of the entorhinal and perirhinal cortices in the non-human primate as shown by PET. Implications for Alzheimer's disease

Temporoparietal glucose hypometabolism, neuronal loss in the basal forebrain cholinergic structures and preferential accumulation of neurofibrillary tangles in the rhinal cortex (i.e. in the entorhinal and perirhinal cortices) are three early characteristics of Alzheimer's disease. Based on studies of the effects of neurotoxic lesions in baboons, we previously concluded that damage to the cholinergic structures plays, at best, a marginal role in the association neocortex hypometabolism of Alzheimer's disease. In the present study, we have assessed the remote metabolic effects of bilateral neurotoxic lesions of both entorhinal and perirhinal cortices. Using coronal PET coregistered with MRI, the cerebral metabolic rate for glucose (CMR(glc)) was measured before surgery and sequentially for 2-3 months afterward (around days 30, 45 and 80). Compared with sham-operated baboons, the lesioned animals showed a significant and long-lasting CMR(glc) decline in a small set of brain regions, especially in the inferior parietal, posterior temporal, posterior cingulate and associative occipital cortices, as well as in the posterior hippocampal region, all of which also exhibit glucose hypometabolism in Alzheimer's disease. Remarkably, the degree of CMR(glc) decline in four of these regions significantly correlated with the severity of histologically determined damage in the rhinal cortex, strongly supporting the specificity of the observed metabolic effects. There were also differences between the metabolic pattern observed in the lesioned animals and that classically reported in Alzheimer's disease; for instance, the hypometabolism we found in the stratum has not been reported in early Alzheimer's disease, although this structure can be affected in late stages of the disease and has direct anatomical connections with the rhinal cortex. Nevertheless, this study shows for the first time that the temporoparietal and hippocampal hypometabolism found in Alzheimer's disease may partly result from neuroanatomical disconnection with the rhinal cortex. This, in turn, further strengthens the hypothesis that neuronal damage and dysfunction in the rhinal cortices play a major role in the expression of Alzheimer's disease.

Effects of damage to the basal forebrain on brain glucose utilization: a reevaluation using positron emission tomography in baboons with extensive unilateral excitotoxic lesion

Neuronal loss in the basal forebrain cholinergic structures and frontotemporal hypometabolism are two characteristics of Alzheimer's disease, but their interrelations still are unsettled. We previously reported that unilateral electrolytic lesions of the nucleus basalis of Meynert in baboons were associated with marked but transient cortical hypometabolism. The current study reevaluates this issue using improved methodology. Baboons with unilateral ibotenic acid lesion of all three basal forebrain cholinergic structures (IBO group) were compared with sham-operated animals. The CMRglc was measured with high-resolution coronal positron emission tomography scanning coregistered with magnetic resonance imaging, before surgery and serially between 4 and 72 days afterward. Severe histologic basal forebrain damage and a decrease of more than 50% in cortical choline acetyltransferase activity were found postmortem in the IBO group. Transient and nonspecific hypometabolism was found in the needle track area in both groups. Compared with the sham-operated group, only marginally significant decreases in ipsilateral-contralateral CMRglc ratios were observed in the IBO group, affecting only 1 of 14 neocortical areas investigated (the anterior temporal cortex) at a single postsurgical time (day 14), and the posterior hippocampal region at days 14 and 38. Furthermore, there was no consistently significant correlation between ipsilateral-contralateral CMRglc ratios and cortical choline acetyltransferase activity values in any of the four regions analyzed. These results suggest that cholinergic deafferentation play at best a marginal role in the brain hypometabolism observed in Alzheimer's disease.

EEG coherence in Alzheimer's disease

EEG coherence can be used to evaluate the functionality of cortical connections and to get information about the synchronization of the regional cortical activity. We studied EEG coherence in patients affected by clinically probable Alzheimer's disease (AD) in order to quantify the modifications in the cortico-cortical or cortico-subcortical connections. The EEGs were recorded in 10 AD patients (with mild or moderate degrees of dementia) and in 10 normal age-matched subjects, at rest and eye-closed, from 16 electrodes with linked-ears reference. Spectral parameters and coherence were calculated by a multichannel autoregressive model using 50 artifact-free epochs, 1 s duration each. Alpha coherence was significantly decreased in 6 patients, the decrease being more accentuated in the area near the electrode taken into account; a significant delta coherence increase was found in a few patients between frontal and posterior regions. The AD group showed a significant decrease of alpha band coherence, in particular in temporo-parieto-occipital areas, more evident in patients with a more severe cognitive impairment. These abnormalities could reflect two different pathophysiological changes: the alpha coherence decrease could be related to alterations in cortico-cortical connections, whereas the delta coherence increase could be related to the lack of influence of subcortical cholinergic structures on cortical electrical activity.

Variability of cerebral blood flow deficits in 99mTc-HMPAO SPECT in patients with Alzheimer's disease

The purpose of this study was to analyse the frequency of the different pathological perfusion patterns in SPECT in a clinical, unselected population of patients with Alzheimer's disease. In 91 patients and 16 control subjects regional cerebral blood flow (rCBF) was measured with Single Photon Emission Computed Tomography (SPECT) using 99mTc-hexa-methyl-propyleneamine oxime (HMPAO). 95% confidence intervals obtained from the perfusion values of the control subjects were used to define normal perfusion ranges. The frequency of perfusion deficits in the left frontal, temporal, parietal and occipital lobes were 62.2%, 60.4%. 70.3% and 23.1%, respectively. In the right hemisphere the corresponding values were 60.4%, 58.2%, 63.7% and 9.9%. With the exception of the occipital lobes these frequencies were not significantly different. The analysis of the perfusion pattern of each patient revealed 35 different combinations of lobes with perfusion deficits. The temporo-parietal perfusion deficits were not more frequent than the temporofrontal perfusion deficits. These results suggest that in the clinical routine a high variety of heterogeneous rCBF patterns have to be expected.

Decreased brain glucose metabolism in microvessels from patients with Alzheimer's disease

We studied brain glucose metabolism in patients with Alzheimer's disease and age-matched controls in vivo by PET and assessed brain glucose utilization and the phosphorylation constant K3 for hexokinase. In addition we determined in vitro the binding of 2DG and measured its phosphorylation to 2DG-phosphate in cerebral microvessels obtained at autopsy from subjects with Alzheimer's disease and age-matched controls. In patients with Alzheimer's disease we found a marked decrease in the kinetic constant K3 for the hexokinase, and a marked decrease in the overall metabolism of glucose in our PET studies; in microvessels there was a marked decrease in the affinity of 2DG and a decrease in hexokinase activity. Alzheimer's disease may be related to a complex alteration in brain glucose metabolism.

Decreased cortical glucose metabolism correlates with hippocampal atrophy in Alzheimer's disease as shown by MRI and PET

OBJECTIVE

To investigate the relation between atrophy of the hippocampus and parahippocampal gyrus (the % hippocampal area) and cerebral metabolic rate for glucose (CMRGlc) in Alzheimer's disease.

METHODS

13 patients with probable Alzheimer's disease by NINCDS-ADRDA criteria (six men; seven women, mean age 71 years, mini mental state 13.8 (SD 4.6)) and age matched controls were studied. T1 weighted MRI (0.5T) images were used for evaluation of the hippocampal area. With a digitiser system, a percentage of the hippocampal area to the brain (the % hippocampal area) was calculated. Eight patients received another T1 weighted MRI (1.5T) for further evaluation of the minimum thickness of the hippocampus. Regional CMRGlc (rCMRGlc) was measured using PET and the FDG technique.

RESULTS

The hippocampal area in patients with Alzheimer's disease was significantly lower than that of controls (P < 0.01). All the cortical rCMRGlc values in patients with Alzheimer's disease were lower than those of controls (P < 0.01). A significant correlation (P < 0.05) was found between the % hippocampal area and rCMRGlc in the temporal lobe, temporoparieto-occipital (TPO) region, and frontal lobe in Alzheimer's disease. There was a significant correlation between minimal hippocampal thickness and ipsilateral TPO metabolism on both sides.

CONCLUSION

The ipsilateral correlation between hippocampal atrophy and decreased TPO metabolism in Alzheimer's disease suggests a functional relation and the asymmetries show that Alzheimer's disease is an asymmetric disease in its early stages.

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.

HM-PAO (CERETEC) SPECT brain scanning in the diagnosis of Alzheimer's disease

OBJECTIVE

To evaluate the accuracy of Single Photon Emission Computed Tomography (SPECT) scanning in the diagnosis of Alzheimer's Disease (AD) and its capacity to improve the diagnostic accuracy of conventional clinical evaluation.

DESIGN

Comparison of SPECT scanning of AD and normal subjects with the criterion standard of clinical diagnosis confirmed by 1-year repeated evaluation.

SETTING

A memory clinic in a tertiary care university hospital.

PATIENTS

One hundred twenty patients were evaluated upon entering the Jewish General Hospital (McGill University) Memory Clinic. Fifty-eight patients were diagnosed as having AD and 17 as having vascular dementia. Twenty unmatched controls (recruited mainly through newspaper advertisements) were normal, and 25 had cognitive impairment without dementia (not included in the statistical analysis).

MAIN OUTCOME MEASURES

Comparison of visual inspection of SPECT, based on the system of classification developed by Holman et al., using B pattern alone as positive or B (bilateral posterior temporal and/or parietal cortex deficits) or C (bilateral posterior temporal and/or parietal deficits with additional defects) pattern and B or C or D (unilateral posterior temporal and/or parietal defects with or without additional defects) as positive compared with clinical diagnosis after repeated evaluations. Sensitivity and specificity, as well as positive predictive value (PPV) and negative predictive value (NPV) based on the prevalence of AD in a memory clinic setting of 30% or 50%, were calculated.

RESULTS

With B pattern as positive, the sensitivity of SPECT was 21% whereas the specificity was 80%. With B or C as positive, the sensitivity was 29% and the specificity was 75%. With B or C or D as positive, the sensitivity was 55% and the specificity was 65%. With a 30% prevalence, the PPV with B pattern as positive was 31% whereas the NPV was 30%. The PPV with B or C as positive was 33% while the NPV was 29%, and the PPV with B or C or D as positive was 40% whereas the NPV was 23%. With a 50% prevalence, the PPV with B pattern as positive was 51% and the NPV 49.6%; the PPV with B or C as positive was 54% and the NPV 48.6%; the PPV with B or C or D as positive was 61% while NPV was 41%.

CONCLUSION

The sensitivity and specificity were too low for SPECT to be useful as a diagnostic test for AD. The poor positive and negative predictive values in our tertiary care clinic mean that SPECT is not useful in "ruling-in" or "ruling-out" AD in that setting. In fact, clinical evaluation is more accurate.

Cognitive and neurobiologic markers of early Alzheimer disease

Recent studies indicate that impairments in two cognitive domains characterize the cognitive abnormalities that appear earliest in the course of Alzheimer disease (AD). These cognitive domains pertain to memory and executive function ability; in particular, memory test scores reflecting the difference between immediate and delayed recall and tasks that assess cognitive flexibility (e.g., set-shifting). Preliminary data indicate that tasks of this nature, along with specific genetic information (i.e., APOE-4 status), are important in identifying which individuals with recent cognitive changes (considered to have "questionable" disease) will progress to the point where they meet criteria for AD over time. When this cognitive and genetic information is combined with neuroimaging measures targeted at the brain regions demonstrating pathology early in AD, it may serve as specific and accurate prognostic markers of AD.

Schizophrenia and Alzheimer's disease: clinical and pathophysiologic analogies

Psychotic symptoms are prominent in schizophrenia and a frequent neuropsychiatric manifestation of Alzheimer's disease (AD), occurring in approximately 50% of patients affected. The shared psychiatric symptoms suggest common cerebral pathophysiologies. Radiologic and pathologic findings indicate a predilection toward limbic involvement, with structural and atrophic changes of the medical temporal region predominating in both disorders. Neurochemical alterations affecting the dopaminergic/cholinergic axis appear to be central to both schizophrenia and AD. The basic pathologies of the two disorders are different, but they have similarities in the pattern of regional brain dysfunction, biochemical dysfunction, and symptomatology. We represent a selective review of these similarities. Insights drawn from these observations enrich the understanding of each disorder.

Desensitization of the neuronal insulin receptor: a new approach in the etiopathogenesis of late-onset sporadic dementia of the Alzheimer type (SDAT)?

Even in its incipient stage, late-onset sporadic dementia of the Alzheimer type (SDAT) is characterized by an abnormal reduction in brain glucose consumption and energy formation. Gathering evidence indicates that cerebral glucose metabolism is controlled by brain insulin/insulin receptors. This led us to hypothesize that the abnormal reduction in glucose utilization found in Alzheimer brains is preceded by a desensitization of cerebral insulin receptors which might be due to enhanced levels of stress factors such as cortisol and catecholamines. The hypothesis is supported by clinical findings of an abnormal response to the oral glucose tolerance test in AD patients. Furthermore, experimental desensitization of the cerebral insulin receptor resulted in both cognitive deficits and metabolic abnormalities in cerebral oxidative glucose metabolism resembling those described in incipient late-onset SDAT. Glucose is the major source of energy in the CNS, and any impairment in cerebral glucose oxidation can be expected to result in deficits in both acetylcholine synthesis and ATP formation, which might contribute to altered APP processing and enhanced susceptibility to neurotoxicity.

Primitive reflexes in Alzheimer's disease and vascular dementia

Data on the prevalence and clinical value of primitive reflexes (PRs) in dementia are controversial, mainly due to a lack of standardization of the methods by which these signs are elicited and scored. A standardized protocol was used to investigate eight PRs in 20 patients with Alzheimer's disease (AD), 20 patients with vascular dementia (VD), and 20 control subjects for each group. Both patient groups showed considerably more PRs than the control groups. The prevalence of PRs was related to the severity of dementia. No single reflex or combination of PR pathognomonic for dementia could be distinguished. The PR profile of AD and VD patients were similar.

Canadian guidelines for the development of antidementia therapies: a conceptual summary

The magnitude of the problems faced by Canadian society as a result of an aging population has been identified. Perhaps the most important concern related to this greying of Canada is the increasing incidence of dementia and Alzheimer's disease. Therapeutic options for these disorders have been limited to date. Advances in biotechnology and molecular biology will offer novel approaches to treatment. These and the expansion of more traditional therapeutic avenues require guidelines with the aim of optimizing their development.

Decreased cingulate and precuneate glucose utilization in alcoholic Korsakoff's syndrome

Localized cerebral glucose utilization was determined for nine abstinent alcoholic men with Korsakoff's syndrome and 10 age-matched normal men who underwent positron emission tomography with [18F]2-fluoro-2-deoxyglucose (FDG). Patients with Korsakoff's syndrome showed relatively decreased glucose utilization in cingulate and precuneate areas. These decreases persisted even after correction for group differences in ventricular and sulcal cerebrospinal fluid measured on computed tomography. Electroencephalographic recordings at the time of FDG uptake showed no group differences, a finding that demonstrates that the metabolic differences could not be explained by differences in physiological arousal at the time of scanning. It is concluded that the decreased glucose utilization in the patients reflects a disruption of memory circuitry, the Papez circuit, caused by diencephalic lesions induced by thiamine deficiency.

Metabolic effects of scopolamine and physostigmine in human brain measured by positron emission tomography

Two of the more consistent findings in Alzheimer's disease are depressions in frontal and temporoparietal glucose metabolism and a loss of cholinergic neurons in the nucleus basalis of Meynert. Nonetheless, cholinergic replacement strategies have had only minimal therapeutic successes. Whether this situation reflects the limited contribution of cholinergic deafferentation to the intellectual decline or the meager ability of the pharmaceuticals tested to exert their intended pharmacologic action remains unclear. To address this question, the distribution of cerebral abnormalities found in untreated Alzheimer patients, as revealed by positron emission tomography following 18F-fluorodeoxyglucose, were compared with the pattern of functional changes produced by drugs that block or stimulate cholinergic function. Physostigmine was administered to 6 Alzheimer patients to increase brain cholinergic neurotransmission. The anticholinergic scopolamine, given to normal volunteers, was administered to 6 age-matched controls. These data were compared to those obtained from the same subjects while receiving placebo. Amnestic doses of the anticholinergic, scopolamine increased glucose metabolism by up to 20% (p < 0.001) in all brain regions studied, except thalamus. This response contrasted with the metabolic reductions of up to 17% (p < 0.01), especially in parietal and frontal association cortices, occurring in unmedicated Alzheimer patients. Maximum tolerated doses of the anti-cholinesterase, physostigmine, rather than tending to normalize abnormalities in these patients, further reduced cerebral metabolism (p < 0.01) and increased metabolism in thalamus in a pattern inversely correlated (p < 0.001) with that produced by scopolamine. These results fail to support a cholinergic basis for the abnormal metabolic pattern in Alzheimer's disease.

Evaluation of multiple doses of milacemide in the treatment of senile dementia of the Alzheimer's type

A multicenter, double-blind, placebo-controlled, parallel group study was conducted to assess the safety and efficacy of three doses of milacemide in the treatment of patients with senile dementia of the Alzheimer type of mild to moderate severity. Patients were randomly assigned to receive one of three dosages of milacemide (400, 800, or 1200 mg/day) or placebo for 4 weeks followed by a single-blind 4-week placebo period. One hundred forty-eight men and women older than 50 years of age were enrolled, and 129 patients completed the study. The differences among treatment groups were not statistically different with respect to total scores on the Alzheimer's Disease Assessment Scale or any items and subscales that were examined, nor were significant differences on the Clinical Global Impression Scale found. Clinically significant increases in liver function tests, specifically aspartate aminotransferase and alanine aminotransferase (AST and ALT), were reported for five of the patients receiving milacemide, requiring their withdrawal from the study.

Cerebral blood flow in patients with dementia of Alzheimer's type

In the normal brain as well as in Alzheimer's disease (AD), regional cerebral blood flow (CBF) is coupled to metabolic demand and, therefore, changes in CBF reflect variations in neuronal metabolism. The use of radionuclide techniques, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), provides an accurate assessment of regional functional activity, i.e., CBF and metabolism, and could be very helpful for the differential diagnosis of AD. This disease is characterized by a decrease in global CBF and metabolism. When found, a symmetric bi-parieto-temporal CBF reduction is highly diagnostic for AD, despite the fact that a similar CBF pattern could also be observed in other types of dementia. Many AD patients with parieto-temporal flow reduction also have a diffuse flow reduction in the frontal cortical areas, particularly in advanced stages of the disease. Lateral CBF asymmetry is also very frequent; speech disorders are highly characteristic of left-sided flow reduction, while visuospatial apraxia is dominating in the right-sided cases. In advanced and severe cases of AD, CBF and metabolism tend to be more uniformly reduced throughout the cortex, sparing only the primary visual and sensory-motor cortices. PET and SPECT measurement of brain perfusion and metabolism has added a new dimension to the knowledge of dementia disorders, with a better differential diagnosis between AD and other forms of dementia. The correlation with neuropsychological data has also given new insight into the disease.