Use of structural imaging to study the progression of Alzheimer's disease

Multimodality Imaging Approach in Alzheimer disease. Part I: Structural MRI, Functional MRI, Diffusion Tensor Imaging and Magnetization Transfer Imaging

The authors make a complete review of the potential clinical applications of traditional and novel magnetic resonance imaging (MRI) techniques in the evaluation of patients with Alzheimer's disease, including structural MRI, functional MRI, diffusion tension imaging and magnetization transfer imaging.

MTA index: a simple 2D-method for assessing atrophy of the medial temporal lobe using clinically available neuroimaging

Background and purpose: Despite a strong correlation to severity of AD pathology, the measurement of medial temporal lobe atrophy (MTA) is not being widely used in daily clinical practice as a criterion in the diagnosis of prodromal and probable AD. This is mainly because the methods available to date are sophisticated and difficult to implement for routine use in most hospitals—volumetric methods—or lack objectivity—visual rating scales. In this pilot study we aim to describe a new, simple and objective method for measuring the rate of MTA in relation to the global atrophy using clinically available neuroimaging and describe the rationale behind this method.

Description: This method consists of calculating a ratio with the area of 3 regions traced manually on one single coronal MRI slide at the level of the interpeduncular fossa: (1) the medial temporal lobe (MTL) region (A); (2) the parenchima within the medial temporal region, that includes the hippocampus and the parahippocampal gyrus—the fimbria taenia and plexus choroideus are excluded—(B); and (3) the body of the ipsilateral lateral ventricle (C). Therefrom we can compute the ratio “Medial Temporal Atrophy index” at both sides as follows: MTAi = (A − B)× 10/C.

Conclusions: The MTAi is a simple 2D-method for measuring the relative extent of atrophy in the MTL in relation to the global brain atrophy. This method can be useful for a more accurate diagnosis of AD in routine clinical practice. Further studies are needed to assess the usefulness of MTAi in the diagnosis of early AD, in tracking the progression of AD and in the differential diagnosis of AD with other dementias.

Restoration of dietary-fat induced blood-brain barrier dysfunction by anti-inflammatory lipid-modulating agents

BACKGROUND

Several studies have identified use of non-steroidal-anti-inflammatory drugs and statins for prevention of dementia, but their efficacy in slowing progression is not well understood. Cerebrovascular disturbances are common pathological feature of Alzheimer's disease. We previously reported chronic ingestion of saturated fatty acids (SFA) compromises blood-brain barrier (BBB) integrity resulting in cerebral extravasation of plasma proteins and inflammation. However, the SFA-induced parenchymal accumulation of plasma proteins could be prevented by co-administration of some cholesterol lowering agents. Restoration of BBB dysfunction is clinically relevant, so the purpose of this study was to explore lipid-lowering agents could reverse BBB disturbances induced by chronic ingestion of SFA's.

METHODS

Wild-type mice were fed an SFA diet for 12 weeks to induce BBB dysfunction, and then randomised to receive atorvastatin, pravastatin or ibuprofen in combination with the SFA-rich diet for 2 or 8 weeks. Abundance of plasma-derived immunoglobulin-G (IgG) and amyloid-β enriched apolipoprotein (apo)-B lipoproteins within brain parenchyme were quantified utilising immunofluorescence microscopy.

RESULTS

Atorvastatin treatment for 2 and 8 weeks restored BBB integrity, indicated by a substantial reduction of IgG and apo B, particularly within the hippocampus. Pravastatin, a water-soluble statin was less effective than atorvastatin (lipid-soluble). Statin effects were independent of changes in plasma lipid homeostasis. Ibuprofen, a lipid-soluble cyclooxygenase inhibitor attenuated cerebral accumulation of IgG and apo B as effectively as atorvastatin. Our findings are consistent with the drug effects being independent of plasma lipid homeostasis.

CONCLUSION

Our findings suggest that BBB dysfunction induced by chronic ingestion of SFA is reversible with timely introduction and sustained treatment with agents that suppress inflammation.

Sex and age differences in atrophic rates: an ADNI study with n=1368 MRI scans

We set out to determine factors that influence the rate of brain atrophy in 1-year longitudinal magnetic resonance imaging (MRI) data. With tensor-based morphometry (TBM), we mapped the 3-dimensional profile of progressive atrophy in 144 subjects with probable Alzheimer's disease (AD) (age: 76.5 +/- 7.4 years), 338 with amnestic mild cognitive impairment (MCI; 76.0 +/- 7.2), and 202 healthy controls (77.0 +/- 5.1), scanned twice, 1 year apart. Statistical maps revealed significant age and sex differences in atrophic rates. Brain atrophic rates were about 1%-1.5% faster in women than men. Atrophy was faster in younger than older subjects, most prominently in mild cognitive impairment, with a 1% increase in the rates of atrophy and 2% in ventricular expansion, for every 10-year decrease in age. TBM-derived atrophic rates correlated with reduced beta-amyloid and elevated tau levels (n = 363) at baseline, baseline and progressive deterioration in clinical measures, and increasing numbers of risk alleles for the ApoE4 gene. TBM is a sensitive, high-throughput biomarker for tracking disease progression in large imaging studies; sub-analyses focusing on women or younger subjects gave improved sample size requirements for clinical trials.

Alzheimer's disease therapeutic research: the path forward

The field of Alzheimer's disease therapeutic research seems poised to bring to clinic the next generation of treatments, moving beyond symptomatic benefits to modification of the underlying neurobiology of the disease. But a series of recent trials has had disappointingly negative results that raise questions about our drug development strategies. Consideration of ongoing programs demonstrates difficult pitfalls. But a clear path forward is emerging. Successful strategies will utilize newly available tools to reconsider issues of diagnosis, assessment and analysis, facilitating the study of new treatments at early stages in the disease process at which they are most likely to yield major clinical benefits.

Alzheimer's disease: from pathology to therapeutic approaches

Mind how you go: The current strategies for the development of therapies for Alzheimer's disease are very diverse. Particular attention is given to the search for inhibitors (see picture for two examples) of the proteolytic enzyme beta- and gamma-secretase, which inhibits the cleavage of the amyloid precursor proteins into amyloid beta peptides, from which the disease-defining deposits of plaque in the brains of Alzheimer's patients originates.Research on senile dementia and Alzheimer's disease covers an extremely broad range of scientific activities. At the recent international meeting of the Alzheimer's Association (ICAD 2008, Chicago) more than 2200 individual scientific contributions were presented. The aim of this Review is to give an overview of the field and to outline its main areas, starting from behavioral abnormalities and visible pathological findings and then focusing on the molecular details of the pathology. The "amyloid hypothesis" of Alzheimer's disease is given particular attention, since the majority of the ongoing therapeutic approaches are based on its theoretical framework.

Vitamin B-12 and cognition in the elderly

Vitamin B-12 deficiency is often associated with cognitive deficits. Here we review evidence that cognition in the elderly may also be adversely affected at concentrations of vitamin B-12 above the traditional cutoffs for deficiency. By using markers such as holotranscobalamin and methylmalonic acid, it has been found that cognition is associated with vitamin B-12 status across the normal range. Possible mediators of this relation include brain atrophy and white matter damage, both of which are associated with low vitamin B-12 status. Intervention trials have not been adequately designed to test whether these associations are causal. Pending the outcome of better trials, it is suggested that the elderly in particular should be encouraged to maintain a good, rather than just an adequate, vitamin B-12 status by dietary means.

Colostrinin: a naturally occurring compound derived from mammalian colostrum with efficacy in treatment of neurodegenerative diseases, including Alzheimer's

Neurodegenerative illnesses such as Alzheimer's disease and their debilitating effects pose a major problem as their incidence increases. Although clinical management of neurodegenerative diseases usually involves symptomatic treatment, Colostrinin() (CLN), which has efficacy in counteracting neural degradation and in stimulating neural growth, might prove to be a more effective means to deal with the causes of Alzheimer's and other neurodegenerative diseases. Evidence for the clinical efficacy of CLN is discussed and recent data examined showing the remarkable ability of CLN to reduce oxidative stress, prevent beta-amyloid aggregation and prolong the lifespan in a laboratory model of premature ageing. An increasingly important application for CLN has been as a nutraceutical product for use in the early stages of cognitive decline in humans, with licensed use in North America and Australia, and now in Europe. It might also be of considerable utility as a veterinary nutraceutical for companion animals.

Diagnosis and treatment of dementia: 3. Mild cognitive impairment and cognitive impairment without dementia

BACKGROUND

Mild cognitive impairment and cognitive impairment, no dementia, are emerging terms that encompass the clinical state between normal cognition and dementia in elderly people. Controversy surrounds their characterization, definition and application in clinical practice. In this article, we provide physicians with practical guidance on the definition, diagnosis and treatment of mild cognitive impairment and cognitive impairment, no dementia, based on recommendations from the Third Canadian Consensus Conference on the Diagnosis and Treatment of Dementia, held in March 2006.

METHODS

We developed evidence-based guidelines using systematic literature searches, with specific criteria for study selection and quality assessment, and a clear and transparent decision-making process. We selected studies published from January 1996 to December 2005 that had mild cognitive impairment or cognitive impairment, no dementia, as the outcome. Subsequent to the conference, we searched for additional articles published between January 2006 and January 2008. We graded the strength of evidence using the criteria of the Canadian Task Force on Preventive Health Care.

RESULTS

We identified 2483 articles, of which 314 were considered to be relevant and of good or fair quality. From a synthesis of the evidence in these studies, we made 16 recommendations. In brief, family physicians should be aware that most types of dementia are preceded by a recognizable phase of mild cognitive decline. They should be familiar with the concepts of mild cognitive impairment and of cognitive impairment, no dementia. Patients with these conditions should be closely monitored because of their increased risk for dementia. Leisure activities, cognitive stimulation and physical activity could be promoted as part of a healthy lifestyle in elderly people and those with mild cognitive impairment. Vascular risk factors should be treated optimally. No other specific therapies can yet be recommended.

INTERPRETATION

Physicians will increasingly see elderly patients with mild memory loss, and learning an approach to diagnosing states such as mild cognitive impairment is now warranted. Close monitoring for progression to dementia, promotion of a healthy lifestyle and treatment of vascular risk factors are recommended for the management of patients with mild cognitive impairment.

Neuropsychological correlates of whole brain atrophy in Alzheimer's disease

Alzheimer's disease (AD) is associated with excess whole brain volume loss, and progressive cognitive impairment. We aimed to study the extent to which these two potential biomarkers of AD progression are correlated. Forty-six patients with sporadic AD were tested with a neuropsychometric battery including test of verbal and visual memory, vocabulary, arithmetic, naming, visuoperceptual skills and reasoning at two time-points, approximately 1 year apart; annualised rates of change for each test were calculated. Each subject also attended for up to twelve T1-weighted volumetric MRI scans at fixed intervals over a 2-year period. For each individual all possible scan-pairs were positionally registered, and whole brain atrophy rates were calculated using the brain boundary shift integral. Linear mixed models were used to investigate associations between atrophy rate and coincident change in each neuropsychometric score. Each model estimated the effect of a unit change in score, plus the additional effect of a fall to floor, after adjusting for baseline levels. 467 MRI scans were performed, permitting 2199 individual measures of change to be made. The model-derived mean atrophy rate was 2.23% per year with a between-subject SD of 0.99% per year. Increasing atrophy rate was significantly associated with rate of change in a number of non-memory based neuropsychological scores, with the strongest association seen with longitudinal change in matrix reasoning (p=0.004). These results provide further evidence that cerebral atrophy is a clinically relevant marker of AD progression. This methodology whereby data from patients falling to floor on a given test may be included and accounted for, rather than discarded, may find broader application in clinical studies incorporating neuropsychometric outcomes.

Combining short interval MRI in Alzheimer's disease: Implications for therapeutic trials

Cerebral atrophy calculated from serial MRI is a marker of Alzheimer's disease (AD) progression, and a potential outcome measure for therapeutic trials. Reducing within-subject variability in cerebral atrophy rates by acquiring more than two serial scans could allow for shorter clinical trials requiring smaller patient numbers. Forty-six patients with AD and 23 controls each had up to 10 serial MR brain scans over two years. Whole brain atrophy was calculated for each subject from every scan-pair. 708 volumetric MRI scans were acquired: 2199 measures of atrophy were made for patients, and 1182 for controls. A linear mixed model was used to characterise between and within-individual variability. These results were used to investigate the power of combining multiple serial scans in treatment trials of varying lengths. In AD, the mean whole brain atrophy rate was 2.23%/year (95% CI: 1.90-2.56%/year). The linear mixed model was shown to fit the data well and led to a formula (0.99(2) + (0.82/t)2) for the variance of atrophy rates calculated from two scans "t" years apart. Utilising five optimally timed scans with repeat scans at each visit reduced the component of atrophy rate variance attributable to within-subject variability by approximately 56%, equating to a approximately 40% sample size reduction (228 vs 387 patients per arm to detect 20% reduction in atrophy rate) in a six-month placebo-controlled trial. This benefit in terms of sample size is relatively reduced in longer trials, although adding extra scanning visits may have benefits when patient drop-outs are accounted for. We conclude that sample sizes required in short interval therapeutic trials using cerebral atrophy as an outcome measure may be reduced if multiple serial MRI is performed.

Neuronal plasticity in memory and learning abilities: theoretical position and selective review

Neural plasticity of modality-nonspecific and modality-specific memory and learning abilities pertains to fluid intelligence and crystallized intelligence, respectively. The limbic system with the novelty neurons of the hippocampus interacts with the prefrontal cortex optimization of the orienting reflex and voluntary attention. Brain-derived neurotrophic factor produced by novelty neurons of the hippocampus contributes to long-term memory formation and improves learning abilities in a wide range of disciplines. Synergistic combination of stimulation with "analytical-specific visual perceptual patterns" and "optimally high" physiological activation of the bilateral electrodermal system optimizes the limbic system and prefrontal cortex activity as demonstrated by enhanced prefrontal N450 ERPs to a memory workload paradigm. This is accompanied by improvements in auditory retention tasks, word memorization, higher school achievement and marks, and an amelioration of "analytical-specific perceptual skills" as measured by the Mangina-Test. Intracerebral ERPs to a memory workload paradigm contributed to the elucidation of limbic structures and neocortical sites involved in memory workload processes. The progressive degeneration of these same structures causes the gradual decline of memory functions observed in early Alzheimer's disease. Research findings indicate that ERPs elicited by a memory workload paradigm are sensitive markers for diagnosis, treatment and clinical follow-up of early Alzheimer's patients. In addition, ERPs provide objective measurement of cholinergic medication effects on cerebral functions involved in memory processes through neuropsychophysiological parameters.

Medical imaging in pharmaceutical clinical trials: what radiologists should know

The role of medical imaging in pharmaceutical clinical trials includes identification of likely responders; detection and diagnosis of lesions and evaluation of their severity; and therapy monitoring and follow-up. Nuclear imaging techniques such as PET can be used to monitor drug pharmacokinetics and distribution and study specific molecular endpoints. In assessing drug efficacy, imaging biomarkers and imaging surrogate endpoints can not only be more objective and faster to measure than clinical outcomes, but also allow small group sizes, quick results and good statistical power. In this article some basic principles of drug clinical development are explained. Study design, image reading and quantitative image processing in clinical trials with imaging components are discussed.

Mapping hippocampal and ventricular change in Alzheimer disease

We developed an anatomical mapping technique to detect hippocampal and ventricular changes in Alzheimer disease (AD). The resulting maps are sensitive to longitudinal changes in brain structure as the disease progresses. An anatomical surface modeling approach was combined with surface-based statistics to visualize the region and rate of atrophy in serial MRI scans and isolate where these changes link with cognitive decline. Sixty-two [corrected] high-resolution MRI scans were acquired from 12 AD patients (mean [corrected] age +/- SE at first scan: 68.7 +/- 1.7 [corrected] years) and 14 matched controls (age: 71.4 +/- 0.9 years) [corrected] each scanned twice (1.9 +/- 0.2 [corrected] years apart, when all subjects are pooled [corrected] 3D parametric mesh models of the hippocampus and temporal horns were created in sequential scans and averaged across subjects to identify systematic patterns of atrophy. As an index of radial atrophy, 3D distance fields were generated relating each anatomical surface point to a medial curve threading down the medial axis of each structure. Hippocampal atrophic rates and ventricular expansion were assessed statistically using surface-based permutation testing and were faster in AD than in controls. Using color-coded maps and video sequences, these changes were visualized as they progressed anatomically over time. Additional maps localized regions where atrophic changes linked with cognitive decline. Temporal horn expansion maps were more sensitive to AD progression than maps of hippocampal atrophy, but both maps correlated with clinical deterioration. These quantitative, dynamic visualizations of hippocampal atrophy and ventricular expansion rates in aging and AD may provide a promising measure to track AD progression in drug trials.

Imaging is superior to cognitive testing for early diagnosis of Alzheimer’s disease

Alzheimer's disease (AD) starts at a molecular level possibly decades earlier than could be detected by neuropsychological tests (NPTs). Neuropathological and neuroimaging data suggest that amyloid accumulation precedes the clinical onset of AD. Disease-modifying agents would have to be used early to alter the course of AD. Therefore, preclinical diagnosis is necessary. Structural and functional neuroimaging are superior for detection of the earliest stages of AD. Magnetic resonance imaging (MRI) and positron emission tomography (PET) techniques, including amyloid visualization, will have therapeutic importance for prevention as well as intervention as further refinements of current imaging techniques and biochemical markers occur. Neuropsychological tests measure the effect of pathology for an individual based upon norms obtained from an artificial population-often white and relatively highly educated. Unless serial NPTs are performed, the individual is compared to a population to which they may not conform. Neuroimaging can provide objective measures of preclinical disease state and, when measured serially, rate of change. Such information can be used in prevention trials.

Comparison of methods for measuring longitudinal brain change in cognitive impairment and dementia

PURPOSE

The goal of this project was to compare MRI measures of hippocampal, entorhinal cortex (ERC), and whole brain longitudinal change in cognitively normal elderly controls (C), non-demented subjects with cognitive impairment (CI), and demented (D) subjects.

METHODS

16 C, 6 CI, and 7 D subjects of comparable age were studied with MRI twice, at least 1 year apart. Longitudinal change in total brain size was measured by several methods, including computerized segmentation, non-linear warping, and change in the fluid/tissue boundaries between cerebrospinal fluid (CSF) and brain. Change in hippocampal volume was measured by semi-automated methods, and ERC volumes were manually measured.

RESULTS

The annual rate of atrophy was greater in D versus C and D versus CI for cortical gray matter (cGM) (P=0.009 and 0.002), hippocampus (P=0.0001 and 0.002), and for the change in the fluid/tissue boundary (P=0.03 and 0.03). The annual rate of atrophy of ERC was greater in both CI and D versus C (P=0.01 and 0.0002). No significant differences between groups were found using non-linear warping.

CONCLUSIONS

In CI, the greatest annual rates of atrophy were in ERC, while in D the greatest annual rates of atrophy were in hippocampus and cortex. Progressive ERC atrophy was observed with a greater degree of cognitive impairment, while hippocampal and cortical atrophy were only observed in demented subjects.

Early diagnosis of Alzheimer's disease: contribution of structural neuroimaging

To accurately predict the development of Alzheimer's disease (AD) at its predementia stage would be a major breakthrough from both therapeutic and research standpoints. In this review, our focus is on markers obtained with structural imaging--especially magnetic resonance imaging (MRI)--and on studies of subjects at risk of developing AD. Among the latter, amnestic mild cognitive impairment (MCI) is currently the most commonly accepted reference, and therefore is specially targeted in this review. MCI refers to patients with significant but isolated memory impairment relative to subjects of identical age. Consistent with established histopathological data, structural imaging studies comparing patients with early probable AD to healthy aged subjects have shown that the most specific and sensitive features of AD at this stage are hippocampal and entorhinal cortex atrophy, especially when combined with a reduced volume of the temporal neocortex. MCI patients have significant hippocampal atrophy when compared to aged normal controls. When comparing patients with probable AD to MCI subjects, hippocampal region atrophy significantly extends to the neighboring temporal association neocortex. However, only longitudinal studies of MCI subjects are suited to assess (in a retrospective way) the predictive value of initial atrophy measurements for progression to AD. Few such studies have been published so far and for the most they were based on small samples. Furthermore, the comparison among studies is clouded by differences in both populations studied and MRI methodology used. Nevertheless, comparing the initial MRI data of at-risk subjects who convert to AD at follow-up to those of nonconverters suggests that a reduced association temporal neocortex volume combined with hippocampal or anterior cingulate cortex atrophy may be the best predictor of progression to AD. These data, although still preliminary, are consistent with postmortem studies describing the hierarchical progression of tau lesions in normal aging and early stages of AD, such that damage to the medial temporal lobe and association cortex would account for the memory and nonmemory cognitive impairments, respectively, the combination of which is required to operationally define probable AD. Future research in this field should capitalize on thorough methodology for brain structure delineation, and combine atrophy measurements to cognitive and/or functional imaging data.

Patients with vascular dementia due to microvascular pathology have significant hippocampal neuronal loss

BACKGROUND

Alzheimer's disease (AD) is characterised by functional impairment, cerebral atrophy, and degeneration of specific neuronal populations, especially pyramidal neurones of the cerebral cortex and hippocampal formation. Although patients with subcortical vascular dementia have been shown to have similar metabolic and volumetric deficits to those with AD, the underlying pathogenesis of these changes is poorly understood.

OBJECTIVE

To determine whether pyramidal cell loss occurs in small vessel disease (SVD) dementia by quantifying hippocampal volume and CA1 neurone number.

METHODS

Fifty four prospectively studied patients with dementia were screened, and four patients fulfilling criteria for SVD with no other significant neuropathological abnormality were identified. These were compared with five patients fulfilling criteria for AD and seven controls matched for age and sex. The hippocampal formation was serially sectioned, and the number of CA1 pyramidal neurones estimated using the optical dissector technique. Analysis of variance was used to evaluate group differences.

RESULTS

Patients in both the AD and SVD groups showed a substantial loss of pyramidal neurones from the CA1 region. The pattern of hippocampal atrophy and the degree of CA1 neuronal loss were similar in the two dementia groups.

CONCLUSIONS

These findings support recent in vivo studies showing similar metabolic deficits and atrophy in AD and subcortical vascular dementia. In addition, they provide evidence that the underlying cause of these abnormalities is a similar loss of neurones. Whereas the cause of the neuronal loss in AD is related to the deposition of abnormal proteins, the cause in SVD is unknown. In the absence of other pathologies, damage to cerebral microvasculature should be considered a likely candidate.

Antemortem MRI findings correlate with hippocampal neuropathology in typical aging and dementia

OBJECTIVES

To assess the diagnostic specificity of MRI-defined hippocampal atrophy for AD among individuals with a variety of pathologically confirmed conditions associated with dementia as well as changes attributable to typical aging, and to measure correlations among premortem MRI measurements of hippocampal atrophy, mental status examination performance, and the pathologic stage of AD.

METHODS

An unselected series of 67 individuals participating in the Mayo Alzheimer's Disease Research Center/Alzheimer's Disease Patient Registry who had undergone a standardized antemortem MRI study and also postmortem examination were identified. Hippocampal volumes were measured from antemortem MRI. Each postmortem specimen was assigned a pathologic diagnosis and in addition, the severity of AD pathology was staged using the method of Braak and Braak.

RESULTS

Individuals with an isolated pathologic diagnosis of AD, hippocampal sclerosis, frontotemporal degeneration, and neurofibrillary tangle--only degeneration usually had substantial hippocampal atrophy, while those with changes of typical aging did not. Among all 67 subjects, correlations (all p < 0.001) were observed between hippocampal volume and Braak and Braak stage (r = -0.39), between hippocampal volume and Mini-Mental State Examination (MMSE) score (r = 0.60), and between MMSE score and Braak and Braak stage (r = -0.41).

CONCLUSIONS

Hippocampal atrophy, while not specific for AD, was a fairly sensitive marker of the pathologic AD stage (particularly among subjects with isolated AD pathology [r = -0.63, p = 0.001]) and consequent cognitive status.

Alzheimer's disease: its diagnosis and pathogenesis

A hypothesis has been presented that links many of the identified and putative risk factors for AD and suggests a mechanism for their action. Crawford (1996, 1998) proposes an association between AD and cerebral blood flow (CBF) by citing evidence that many of the factors that are linked with an increased risk of AD also decrease CBF (e.g., old age, depression, underactivity, head trauma). Similarly, it is suggested factors that increase CBF are associated with a decreased risk of AD (e.g., education, exercise, smoking, NSAIDs). Although the authors acknowledge that reduced CBF is not sufficient to cause AD, the reported positive and negative associations provide tantalizing evidence for a common mode of action for many of the equivocal risk factors reported to date. This hypothesis is also consistent with other data that links microvascular damage and impaired blood flow (de la Torre, 1997, 2000) and low education with increased cerebrovascular disease (Del Ser et al., 1999). Gaining a better understanding of the interaction between AD and vascular disease is of great importance. Not only will it provide insights into the pathogenesis of AD, but it may also provide us with a rare opportunity for the treatment and possible prevention of AD. A great many risk factors for vascular disease have been identified and intervention programs have successfully reduced the incidence of heart disease and stroke. The potential exists to provide the same level of success with AD.

Relations between hypometabolism in the posterior association neocortex and hippocampal atrophy in Alzheimer's disease: a PET/MRI correlative study

OBJECTIVES

Hippocampal atrophy and hypometabolism in the posterior association neocortex are two well known features of Alzheimer's disease. A correlation between these two features was reported twice previously, suggesting intriguing relations. This question has been reassessed, this time controlling for severity of dementia as well as assessing each side of the brain separately and using a voxel based image analysis in addition to the previously employed regions of interest (ROIs).

PATIENTS AND METHODS

Eleven patients were studied with probable Alzheimer's disease and mild to moderate dementia in whom both volume MRI and PET assessed cerebral glucose consumption (CMRGlc) were available. Hypothesis driven correlations between hippocampal width (an index of atrophy) and CMRGlc were performed for two posterior association regions, the superior temporal and the inferior parietal (angular gyrus) cortices, using ROIs set separately for each hemisphere. To confirm significant correlations from the ROIs approach, if any, and to assess their specificity for the posterior association neocortex, CMRGlc image voxel based analysis of correlations with hippocampal width was then carried out.

RESULTS

There was a significant correlation, in the positive-neurobiologically expected-direction, between right hippocampal width and right angular gyrus metabolism (p< 0.01, Spearman), which remained significant with Kendall partial correlation controlling for dementia severity (estimated by mini mental state scores). Statistical non-parametric mapping (SnPM) confirmed this correlation (p< 0.025), and showed a single additional correlation in the right middle temporal gyrus (p< 0.005), which is also part of the posterior association cortex.

CONCLUSION

The findings with both ROIs and voxel based mapping replicate earlier reports of a relation between hippocampal atrophy and ipsilateral association cortex hypometabolism in Alzheimer's disease, and for the first time document that this relation is both region specific and independent of the dementing process itself. Why the correlation was significant only for the right hemisphere is unclear but may be related to the limited sample. Hippocampal-neocortical disconnection due to early and severe medial temporal lobe pathology may at least partly explain the posterior association cortex hypometabolism found in Alzheimer's disease.

In vivo mapping of gray matter loss with voxel-based morphometry in mild Alzheimer's disease

Up till now, the study of regional gray matter atrophy in Alzheimer's disease (AD) has been assessed with regions of interest, but this method is time-consuming, observer dependent, and poorly reproducible (especially in terms of cortical regions boundaries) and in addition is not suited to provide a comprehensive assessment of the brain. In this study, we have mapped gray matter density by means of voxel-based morphometry on T1-weighted MRI volume sets in 19 patients with mild AD and 16 healthy subjects of similar age and gender ratio and report highly significant clusters of gray matter loss with almost symmetrical distribution, affecting mainly and in decreasing order of significance the medial temporal structures, the posterior cingulate gyrus and adjacent precuneus, and the temporoparietal association and perisylvian neocortex, with only little atrophy in the frontal lobe. The findings are discussed in light of previous studies of gray matter atrophy in AD based either on postmortem or neuroimaging data and in relation to PET studies of resting glucose consumption. The limitations of the method are also discussed in some detail, especially with respect to the segmentation and spatial normalization procedures as they apply to pathological brains. Some potential applications of voxel-based morphometry in the study of AD are also mentioned.

Practice parameter: diagnosis of dementia (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology

OBJECTIVE

To update the 1994 practice parameter for the diagnosis of dementia in the elderly.

BACKGROUND

The AAN previously published a practice parameter on dementia in 1994. New research and clinical developments warrant an update of some aspects of diagnosis.

METHODS

Studies published in English from 1985 through 1999 were identified that addressed four questions: 1) Are the current criteria for the diagnosis of dementia reliable? 2) Are the current diagnostic criteria able to establish a diagnosis for the prevalent dementias in the elderly? 3) Do laboratory tests improve the accuracy of the clinical diagnosis of dementing illness? 4) What comorbidities should be evaluated in elderly patients undergoing an initial assessment for dementia?

RECOMMENDATIONS

Based on evidence in the literature, the following recommendations are made. 1) The DSM-III-R definition of dementia is reliable and should be used (Guideline). 2) The National Institute of Neurologic, Communicative Disorders and Stroke--AD and Related Disorders Association (NINCDS-ADRDA) or the Diagnostic and Statistical Manual, 3rd edition, revised (DSM-IIIR) diagnostic criteria for AD and clinical criteria for Creutzfeldt--Jakob disease (CJD) have sufficient reliability and validity and should be used (Guideline). Diagnostic criteria for vascular dementia, dementia with Lewy bodies, and frontotemporal dementia may be of use in clinical practice (Option) but have imperfect reliability and validity. 3) Structural neuroimaging with either a noncontrast CT or MR scan in the initial evaluation of patients with dementia is appropriate. Because of insufficient data on validity, no other imaging procedure is recommended (Guideline). There are currently no genetic markers recommended for routine diagnostic purposes (Guideline). The CSF 14-3-3 protein is useful for confirming or rejecting the diagnosis of CJD (Guideline). 4) Screening for depression, B(12) deficiency, and hypothyroidism should be performed (Guideline). Screening for syphilis in patients with dementia is not justified unless clinical suspicion for neurosyphilis is present (Guideline).

CONCLUSIONS

Diagnostic criteria for dementia have improved since the 1994 practice parameter. Further research is needed to improve clinical definitions of dementia and its subtypes, as well as to determine the utility of various instruments of neuroimaging, biomarkers, and genetic testing in increasing diagnostic accuracy.

The nature of the effect of female gonadal hormone replacement therapy on cognitive function in post-menopausal women: a meta-analysis

We reviewed epidemiological and experimental studies of female gonadal hormone replacement therapy (HRT) on cognitive function in post-menopausal women and carried out meta-analyses. In healthy ageing women, HRT has small and inconsistent effects that include enhancement of verbal memory, abstract reasoning and information processing. Epidemiological studies show larger effects than experimental studies, which is not related to sample size. Important confounds may be that women who start using HRT are healthier than women who do not. Also, controlling for socio-economic status diminishes the effect of HRT. The effects of HRT may depend on the age and type of menopause and the therapeutic intervention used, with the most widely used drug, Premarin, having least effect. However, the effects are independent of mood and climacteric symptom alleviation. There is a paucity of experimental studies that include healthy elderly women. The evidence for an estrogen deficiency in women with dementia and cognitive dysfunction is inconsistent. Nevertheless, epidemiological studies suggest that HRT protects against the development of clinically diagnosed Alzheimer's disease. However, poor recall of HRT use by patients and altered physician behaviour may have confounded the effects. Surprisingly, both healthy and demented women with low education seem to benefit most from HRT. Three recent controlled experimental studies using Premarin showed no effects of HRT in preventing further cognitive decline in women who already have Alzheimer's disease. Duration of treatment seems to play an important role, with beneficial effects declining-and even reversing-with longer treatment in women with Alzheimer's disease.Future research should further investigate the cognitive effect of different HRT preparations, serum estrogen levels, and the interactions of HRT with age, menopausal status and existing protective (e.g. education) and risk factors (e.g. smoking and apolipoprotein E genotype) for cognitive decline and Alzheimer's disease.

Event-related brain potentials to Memory Workload and 'Analytical-Specific Perception' (Mangina-test) in patients with early Alzheimer's Disease and in normal controls

Our previous research with intra-cerebral event-related potentials in conjunction with an original Memory Workload Paradigm has shown that significant load effects for the N4 latency were found only for both amygdalae and the left posterior hippocampus as well as for both anterior neo-cortical regions of the temporal gyri. These same structures are also affected in Alzheimer's Disease. Therefore, based on our previous intra-cerebral findings, our present research was to use our novel Memory Workload Paradigm in conjunction with surface ERPs as neurophysiological markers to tap cerebral regions and functions involved in memory disorders pertaining to early Alzheimer's Disease as opposed to normal memory processes in age-matched normal control subjects. Moreover, the Mangina-Test which measures varying degrees of 'Analytical-Specific Visual Perception' was individually administered to all patients and controls in separate sessions. Results indicate that for the early Alzheimer's Disease group, a significant main effect for memory load was found for the P400 amplitude (F(3,30)=4.52, P<0.02) which was absent in the normal group. In particular, the P400 amplitude was significantly higher on posterior head regions for patients with early Alzheimer's Disease as opposed to age-matched normal subjects (F(7,140)=3.54, P<0.03) which distinguished both groups (F(1,20)=6. 13, P<0.03). For the P400 latency, a significant memory load effect was present only for the normal group (F(3,30)=11.26, P<0.01). The Mangina-Test performance clearly differentiated both groups (F(1, 19)=105.85, P<0.001). The present data provide the first valuable evidence that ERPs to our novel Memory Workload Paradigm are sensitive neurophysiological diagnostic markers which delineate the early clinical brain irregularities underlying early Alzheimer's Disease as opposed to the normal memory processes of age-matched normal subjects. In addition, their use could be valuable for the objective clinical follow-up of therapeutic interventions in early Alzheimer's Disease.

Traumatic brain injury elevates the Alzheimer's amyloid peptide A beta 42 in human CSF. A possible role for nerve cell injury

The increased risk for Alzheimer's Disease (AD) associated with traumatic brain injury (TBI) suggests that environmental insults may influence the development of this age-related dementia. Recently, we have shown that the levels of the beta-amyloid peptide (A beta 1-42) increase in the cerebrospinal fluid (CSF) of patients after severe brain injury and remain elevated for some time after the initial event. The relationships of elevated A beta with markers of blood-brain barrier (BBB) disruption, inflammation, and nerve cell or axonal injury were evaluated in CSF samples taken daily from TBI patients. This analysis reveals that the rise in A beta 1-42 is best correlated with possible markers of neuronal or axonal injury, the cytoskeletal protein tau, neuron-specific enolase (NSE), and apolipoprotein E (ApoE). Similar or better correlations were observed between A beta 1-40 and the three aforementioned markers. These results imply that the degree of brain injury may play a decisive role in determining the levels of A beta 1-42 and A beta 1-40 in the CSF of TBI patients. Inflammation and alterations in BBB may play lesser, but nonetheless significant, roles in determining the A beta level in CSF after brain injury.

The histological validation of post mortem magnetic resonance imaging-determined hippocampal volume in Alzheimer's disease

For 11 AD cases and four normal elderly controls, post mortem volumes of the hippocampal subdivisions were calculated by using magnetic resonance imaging and histological sections. After at least six weeks of fixation in formalin, brains were examined on a 1.5-T Philips Gyroscan imager producing T1-weighted coronal images with a 3-mm slice thickness. Brains were then processed and embedded in paraffin. Serial coronal sections, 3 mm apart and stained with Cresyl Violet, were used for the planimetry and unbiased estimation of the total numbers of neurons in the hippocampal subdivisions. For all 15 cases, magnetic resonance imaging- and histology-based measurements were performed along the whole rostrocaudal extent of the hippocampal formation and included three subvolumes: (i) the hippocampus (CA1-CA4 and the dentate gyrus); (ii) hippocampus/subiculum; and (iii) hippocampus/parahippocampal gyrus. After controlling for shrinkage, strong correlations were found between magnetic resonance imaging and histological measurements for the hippocampus (r = 0.97, P < 0.001), hippocampus/subiculum (r = 0.95, P < 0.001) and hippocampus/parahippocampal gyrus (r = 0.89, P < 0.001). We also calculated the total number of neurons in the hippocampus and hippocampus/subiculum subvolumes. Strong correlations between the magnetic resonance imaging subvolumes and neuronal counts were found for the hippocampus (r = 0.90, P < 0.001) and the hippocampus/subiculum subvolume (r = 0.84, P < 0.001). We conclude that very accurate volumetric measurements of the whole hippocampal formation can be obtained by using a magnetic resonance imaging protocol. Moreover, the strong correlations between magnetic resonance imaging-based hippocampal volumes and neuronal numbers suggest the anatomical validity of magnetic resonance imaging volume measurements.

Neuroanatomy of comorbid schizophrenia and learning disability: a controlled study

BACKGROUND

Reasons for the higher frequency of schizophrenia in learning-disabled populations are uncertain. We investigated the neuroanatomical basis for this phenomenon by structural magnetic resonance imaging (MRI) in patients with learning disability and schizophrenia, learning-disabled patients, and patients with schizophrenia.

METHODS

Age-matched and sex-matched patients with learning disability (20 cases), schizophrenia (25), and both disorders (23) underwent MRI scans of the brain. Whole brain areas and specific regions of interest were examined. 29 normal controls were also scanned.

FINDINGS

The scans of the group with both disorders were closely similar to those of the schizophrenic group, in terms of both general structures and the structure of the amygdala-hippocampus. However, the amygdala-hippocampus was significantly smaller on both sides than that of normal controls (left 4.1 vs 4.5 cm3, p=0.011; right 4.2 vs 4.99 cm3, p<0.0001). The brains of learning-disabled patients were generally smaller than those of the other three groups, but the amygdalohippocampal complexes were larger.

INTERPRETATION

In terms of brain structure, patients with comorbid learning disability and schizophrenia resemble patients with schizophrenia and not those with learning disability. We suggest that the higher frequency of schizophrenia in learning-disabled patients is due to a greater tendency of schizophrenic patients to develop cognitive deficits, and that within the learning-disabled population there may be individuals whose deficits result from undiagnosed schizophrenia.

The prognosis of mild cognitive impairment in the elderly

PURPOSE

To determine whether or not subtypes of intellectual functioning are suitable to predict further cognitive decline in individuals with mild cognitive impairment.

DESIGN

Naturalistic longitudinal study (mean interval 2.7 years).

PATIENTS

41 subjects with mild cognitive impairment who attended a memory clinic.

METHODS

SIDAM, CT, SPECT, and ApoE genotype.

RESULTS

At follow-up, 8 out of 41 patients (19.5%) with MCI had progressed to dementia, 8 patients (19.5%) had improved to normal levels of cognitive functioning, 25 patients (61%) had remained stable within the MCI group. At baseline the two prognostic groups differed significantly with regard to age, memory functions, orientation, and the degree of atrophy of the left medial temporal lobe on CT scan.

CONCLUSION

The majority of MCI patients in this study remained cognitively stable within the observation period. Patients with older age, poorer test performance on memory tasks and orientation deficits are at higher risk of progressive decline to dementia. CT measures of medial temporal lobe atrophy may be a sensitive parameter of group discrimination.

Evolution in the conceptualization of dementia and Alzheimer's disease: Greco-Roman period to the 1960s

Most histories of senile dementia commence with Alois Alzheimer's description in 1906 of the first case of Alzheimer's disease, yet the history of senile dementia before 1906 is quite rich, dating back to the ancient Greek and Roman philosophers and physicians. Over the 2500 years since ancient times, the concept of senile dementia has evolved from a rather vague notion that mental decline occurred inevitably in old age, to become defined today by a distinct set of clinical and pathological features with the potential for treatment and prevention within grasp. Throughout history, many elderly individuals with unpredictable behavior were sequestered in institutions, and the line between mental disorders and senile dementia was hazy at best. The identification of Alzheimer's disease at the onset of the 20th century was a turning point for the understanding of senile dementia, and the concepts and histological findings presented by the early researchers of Alzheimer's disease remain relevant still today. Indeed, these early findings are proving to be a continuing source of insight, as many of the issues debated at the turn of the century remain unresolved still today. This paper thus traces the history of the evolution of our current conceptualization of Alzheimer's disease from the amorphous Greco-Roman concept of age-associated dementia.

Characterization of perforant path lesions in rodent models of memory and attention

Early stage Alzheimer's disease (AD) pathology is associated with neurodegeneration of systems within the temporal cortex, e.g. the entorhinal cortex, perforant pathway and hippocampus. The perforant pathway provides the major neuronal input to the hippocampus from the entorhinal cortex and thus relays multimodal sensory information derived from cortical zones into the hippocampus. The earliest symptoms of AD include cognitive impairments, e.g. deficits in short-term memory and attention. Consequently, we have investigated the effect of bilateral knife cut lesions to the perforant path on cognition in rats using models measuring primarily short-term memory (operant delayed match to position task), attention (serial five-choice reaction time task) and spatial learning (Morris water maze). Rats receiving bilateral perforant path lesions showed normal neurological function and a mild hyperactivity. The lesion produced little effect on attention assessed using the five-choice task. In contrast, animals with equivalent lesions showed a robust delay-dependent deficit in the delayed match to position task. Spatial learning in the water maze task was also severely impaired. The delay-dependent deficit in the match to position task was not reversed by tacrine (3 mg/kg) pretreatment. The present data support a selective impairment of cognitive function following perforant path lesions that was confined to mnemonic rather than attentional processing. These findings complement primate and human studies identifying a critical role of the perforant pathway and associated temporal lobe structures in declarative memory. Degeneration of the perforant pathway is likely to contribute to the mnemonic deficits characteristic of early AD. The failure of tacrine to ameliorate these deficits may be relevant to an emerging clinical literature suggesting that cholinomimetic therapies improve attentional rather than mnemonic function in AD.