The role of routine laboratory studies and neuroimaging in the diagnosis of dementia: a clinicopathological study

Structural Brain Magnetic Resonance Imaging to Rule Out Comorbid Pathology in the Assessment of Alzheimer's Disease Dementia: Findings from the Ontario Neurodegenerative Disease Research Initiative (ONDRI) Study and Clinical Trials Over the Past 10 Years

BACKGROUND/OBJECTIVE

Structural brain magnetic resonance imaging (MRI) is not mandatory in Alzheimer's disease (AD) research or clinical guidelines. We aimed to explore the use of structural brain MRI in AD/mild cognitive impairment (MCI) trials over the past 10 years and determine the frequency with which inclusion of standardized structural MRI acquisitions detects comorbid vascular and non-vascular pathologies.

METHODS

We systematically searched ClinicalTrials.gov for AD clinical trials to determine their neuroimaging criteria and then used data from an AD/MCI cohort who underwent standardized MRI protocols, to determine type and incidence of clinically relevant comorbid pathologies.

RESULTS

Of 210 AD clinical trials, 105 (50%) included structural brain imaging in their eligibility criteria. Only 58 (27.6%) required MRI. 16,479 of 53,755 (30.7%) AD participants were in trials requiring MRI. In the observational AD/MCI cohort, 141 patients met clinical criteria; 22 (15.6%) had relevant MRI findings, of which 15 (10.6%) were exclusionary for the study.

DISCUSSION

In AD clinical trials over the last 10 years, over two-thirds of participants could have been enrolled without brain MRI and half without even a brain CT. In a study sample, relevant comorbid pathology was found in 15% of participants, despite careful screening. Standardized structural MRI should be incorporated into NIA-AA diagnostic guidelines (when available) and research frameworks routinely to reduce diagnostic heterogeneity.

Applicability of the CANTAB-PAL computerized memory test in identifying amnestic mild cognitive impairment and Alzheimer's disease

AIM

To compare the diagnostic accuracy of a computerized test, the CANTAB paired associate learning (PAL) to that of an established and validated noncomputerized test, the CERAD Wordlist Learning task in differentiating between normal aging, aMCI and AD in a cross-sectional design.

METHODS

58 participants were assessed (19 with mild probable AD, 17 aMCI, 22 healthy controls).

RESULTS

The variables found to best discriminate between the three groups were the CANTAB PAL total errors adjusted (p < 0.0001, 81.0% of the cases correctly classified), and CERAD Wordlist Learning Delayed Recall (p < 0.0001, 77.6% of the cases correctly classified). Using both PAL total errors adjusted and Wordlist Learning Delayed Recall, 84.5% of the cases were correctly classified.

DISCUSSION

The results suggest that the CANTAB could be used for screening of AD-typical memory impairment.

Is computed tomography still useful as a neuroimaging tool in psychiatry?

BACKGROUND

Computed tomography (CT) has played a pivotal role in psychiatry from its inception; however with the advent of other high-resolution noninvasive neuroimaging techniques such as MRI, the field has gone through a dramatic transformation.

OBJECTIVE

This article will explore the current role of CT in psychiatry.

METHODS

An extensive search of the published literature (1970 - 2008) was conducted, employing a number of databases and terms relevant to CT and imaging.

RESULTS/CONCLUSION

At present CT is primarily used as a screening tool to exclude intracranial pathology. This is partly because it is widely available and less expensive than other imaging modalities. CT is unable to provide region-specific information like MRI and this has restricted its use in disorders in which functional disturbances are suspected, however it remains the preferred mode of investigation where gross structural abnormalities are suspected.

[Stereology as a tool to estimate brain volume and cortical atrophy in elders with dementia]

INTRODUCTION

stereology is a body of methods that allow unbiased and efficient estimation of geometric quantities defined in arbitrary physical structures. In particular, stereology is a valuable tool to assist neuroimaging in the estimation of morphometric parameters in the brain. Therefore, stereology may confer objectivity in the complementary and diagnostic evaluation of dementia by adding disease by adding quantitative data to clinical evaluation.

OBJECTIVES AND METHODS

our purpose was to illustrate estimation of brain volume and pial surface area by means of quantitative, computer-assisted stereological methods. Both parameters were estimated by means of a vertical design with a single series of parallel Cavalieri sections at a random orientation and perpendicular to a fixed horizontal plane. The sections were obtained by magnetic resonance imaging. Suitable test systems (of test points for volume, and of cycloids for surface area) were superimposed on these sections with the aid of special software.

RESULTS

to explore the statistical error of the volume estimator due to stereological sampling, 5 or 10 systematic sections were used in combination with two test point densities in a ratio of 1:4, so that the workload varied in the proportions 1:2:4:8. The four resulting estimators varied between 986 and 1120 cm(3). The surface area estimators varied between 1947 and 2096 cm(2), with workloads varying in the proportions of 1:2:2.3:4.6.

CONCLUSIONS

stereology is a simple and efficient tool to obtain objective brain volume and surface area estimators that are unbiased by design and accurate at a modest cost. Thus the corresponding methods can effectively assist in diagnostic and follow-up evaluation of elders with dementia.

Structural neuroimaging in the diagnosis of dementia

This article reviews recent use of structural imaging in the diagnosis of dementia and presents evidence-based recommendations approved at the meeting of the Third Canadian Consensus Conference on the Diagnosis and Treatment of Dementia held in Montreal in March, 2006. Although the consensus group concurs that it is possible to specify circumstances in which structural imaging has a role to rule out pathology, it also has a role in ruling in concomitant cerebrovascular disease for patient management.

Cognitive impairment

As populations continue to age, the prevalence of dementia is expected to increase. AD is by far the most common cause of dementia. The clinical course of dementia represents the challenges that this disease presents. There are no truly effective therapies for treating dementia, and the cost effectiveness of ChEIs has been challenged; however, there has been an explosion of information about AD. Evidence-based practice parameters for diagnosis and management of dementia have been developed. There has been an increased interest in the possible prodromal states of dementia, such as MCI. The concept of MCI has risen in prominence in recent years; it is speculated that initiation of therapies early in the course of disease may be needed for them to be effective. Considering the enormous burdens that AD places on individuals and society, disease-modifying treatments for AD are needed desperately. There are promising avenues for the development of potentially disease-modifying therapies for this devastating disease.

Evaluation of Dementia: The Case for Neuroimaging All Mild to Moderate Cases

Introduction: The aim of this study was to assess the usefulness of 4 clinical prediction rules, the neuroimaging guidelines from the Canadian Consensus Conference on Dementia (CCCAD) and the modified Hachinski’s Ischaemic Score (HIS) in identifying patients with suspected dementia who will benefit from neuroimaging. Materials and Methods: Two hundred and ten consecutive patients were referred to the memory clinic in a geriatric unit for the evaluation of possible dementia. Sensitivity, specificity and likelihood ratios (LR) were calculated for each of the prediction rules and the CCCAD guidelines, in terms of their ability to identify patients with significant lesions [defined firstly as space-occupying lesions (SOL) alone and secondly as SOL or strokes] on neuroimaging. Similar analyses were applied for the HIS in the detection of strokes. Results: When considering SOL alone, sensitivities ranged from 28.6% to 100% and specificities ranged from 21.7% to 88.4%. However, when strokes were included in the definition of significant lesions, sensitivities ranged from 16.2% to 79.0% and specificities ranged from 20.9% to 92.4%. The modified HIS had a similarly poor sensitivity and specificity (43.3% and 78.9% respectively). The LR for the clinical decision tools did not support the use of any particular instrument. Conclusions: Clinical decision tools do not give satisfactory guidance for determining the need for neuroimaging patients with suspected dementia, when the detection of strokes, in addition to SOL, is regarded as important. We recommend therefore that neuroimaging be considered for all patients with suspected mild or moderate dementia in whom the potential benefits of any treatment outweigh the potential risks. Key words: Diagnostic medical imaging, Practice guidelines, Sensitivity and specificity

Pathological aging of the brain: an overview

The number of elderly people is increasing rapidly and, therefore, an increase in neurodegenerative and cerebrovascular disorders causing dementia is expected. Alzheimer disease (AD) is the most common cause of dementia. Vascular dementia, dementia with Lewy bodies, and frontotemporal dementia are the most frequent causes after AD, but a large proportion of patients have a combination of degenerative and vascular brain pathology. Characteristic magnetic resonance (MR) imaging findings can contribute to the identification of different diseases causing dementia. The MR imaging protocol should include axial T2-weighted images (T2-WI), axial fluid-attenuated inversion recovery (FLAIR) or proton density-weighted images, and axial gradient-echo T2*-weighted images, for the detection of cerebrovascular pathology. Structural neuroimaging in dementia is focused on detection of brain atrophy, especially in the medial temporal lobe, for which coronal high resolution T1-weighted images perpendicular to the long axis of the temporal lobe are extremely important. Single photon emission computed tomography and positron emission tomography may have added value in the diagnosis of dementia and may become more important in the future, due to the development of radioligands for in vivo detection of AD pathology. New functional MR techniques and serial volumetric imaging studies to identify subtle brain abnormalities may also provide surrogate markers for pathologic processes that occur in diseases causing dementia and, in conjunction with clinical evaluation, may enable a more rigorous and early diagnosis, approaching the accuracy of neuropathology.

Modeling a task that is sensitive to dementia of the Alzheimer's type: individual differences in acquisition of a visuo-spatial paired-associate learning task in rhesus monkeys

Early detection of progressive diseases such as Alzheimer's Disease (AD) is crucial for both the treatment and study of the disease. Performance on a visuo-spatial paired-associates learning (vsPAL) task was recently shown to reliably predict a diagnosis of AD in aged populations. The present study reports the development of this vsPAL task for use in nonhuman primates. Translation of vsPAL to a nonhuman model may provide improved preclinical tools for study of the etiology and treatment of dementia. Twelve young adult male rhesus monkeys were trained to perform the vsPAL task concurrently with tests comprising a nonhuman primate neuropsychological test battery. Monkeys successfully learned to perform vsPAL and did so in a task-difficulty ranked fashion. Despite significant individual differences in capability in the acquisition of the recognition memory aspects of the task, all monkeys evidenced the ability to learn within-trial, i.e. to improve with repeated stimulus-location pairings. These results support the use of vsPAL performance under various challenge conditions to investigate the possible substrates of early cognitive decline in AD. Comparison of performance on vsPAL with performance on other memory tasks in the battery will be of more general use in differentiating mechanisms involved in various aspects of mnemonic function.

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.

Dementia update 2003

Clinical and scientific investigations in the field of dementia expanded greatly in the past two decades. Medline citations that addressed Alzheimer disease (AD), the most common dementing disorder, rose from 78 in 1980 to 987 in 1990 and to 1772 in 2000. Underscoring this increased body of knowledge, three practice parameters on dementia were published in 2001 by the Quality Standards Subcommittee of the American Academy of Neurology. Although some older studies are included for context, this review focuses on selected recent advances in dementia that are relevant for the practicing physician. Topics covered include: 1) diagnosis of dementia; 2) risk factors and biomarkers; 3) mild cognitive impairment; 4) the scientific basis for treatment advances in AD; and 5) other dementing disorders.

Neuroimaging in Alzheimer disease: an evidence-based review

Current clinical criteria (DSM-IIIR and NINCDS-ADRDA) for the diagnosis of dementia and AD are reliable; however, these criteria remain to be validated by clinicians of different levels of expertise at different clinical settings. Structural neuroimaging has an important role in initial evaluation of dementia for ruling out potentially treatable causes. Although CT is the appropriate choice when brain tumors, subdural hematoma, or normal pressure hydrocephalus is suspected, MR imaging is more sensitive to the white-matter changes in vascular dementia. The diagnostic accuracy of PET, SPECT, 1H MRS, and MR volumetry of the hippocampus for distinguishing patients with AD from healthy elderly individuals is comparable to the accuracy of a pathologically confirmed clinical diagnosis. Sensitivity of PET for distinguishing patients with dementia with Lewy bodies from AD, however, is higher than that of clinical evaluation; similarly, SPECT and 1H MRS may be adjuncts to clinical evaluation for distinguishing patients with frontotemporal dementia from those with AD. Neuroimaging is valuable in predicting future development of AD in patients with MCI and in carriers of the ApoE epsilon 4 allele who are at a higher risk of developing AD than are cognitively normal elderly individuals. Quantitative MR techniques (e.g., MR volumetry, DWI, magnetization transfer MR imaging, and 1H MRS) and PET are sensitive to the structural and functional changes in the brains of patients with MCI, and hippocampal volumes on MR imaging are associated with future development of AD in these individuals. PET is also sensitive to the regional metabolic decline in the brains of carriers of the ApoE epsilon 4 allele. The longitudinal decrease of whole brain and hippocampal volumes on MR imaging, NAA levels on 1H MRS, cerebral glucose metabolism on PET, and cerebral blood flow on SPECT are associated with rate of cognitive decline in patients with AD. These neuroimaging markers may be useful for monitoring symptomatic progression in groups of patients with AD for drug trials. Furthermore, antemortem MR-based hippocampal volumes correlate with the pathologic stage of AD, and the rate of hippocampal volume loss on MR imaging correlates with clinical disease progression in the cognitive continuum from normal aging to MCI and to AD. Hence, as an in vivo correlate of pathologic involvement, structural imaging measures are potential surrogate markers for disease progression in patients with established AD and in patients with prodromal AD, who will benefit most from disease-modifying therapies underway.

Dementia: when is it not Alzheimer disease?

The advent of symptomatic therapies for Alzheimer disease has placed increasing emphasis on early diagnosis of the dementia syndrome and its various types. This article reviews the definition and epidemiology of the condition that affects up to 50% of all Americans over the age of 80. Also discussed are the main causes of dementia, focusing on those that are not Alzheimer disease and a diagnostic approach that is based on guidelines recently published by the American Academy of Neurology.

Mixed dementia: epidemiology, diagnosis, and treatment

Alzheimer's disease (AD) and vascular dementia (VaD) are the most frequent causes of dementia in older people. Although AD can be diagnosed with a considerable degree of accuracy, the distinction between isolated AD, VaD, and mixed dementia (MD), where both pathologies coexist in the same patient, remains a controversial issue and one of the most difficult diagnostic challenges. Although MD represents a very frequent pathology, especially in older people, as reported in neuropathological studies, the respective importance of degenerative and vascular lesions, their interaction in the genesis of dementia, and the mere existence of MD are still debated. Accurate diagnosis of MD is of crucial significance for epidemiological purposes and for preventive and therapeutic strategies. Until recently, pharmacological studies have generally focused on pure disease, AD or VaD, and have provided little information on the best therapeutic approach to MD. This article provides an overview of MD in older people. A retrospective review of the recent literature on prevalence, incidence, course, risk factors, diagnosis, and treatment of MD was performed. The article also emphasizes the need for further studies, including neuropsychological and functional evaluations, and neuroimaging and clinicopathological correlations to develop a better understanding of MD, which appears to be one of the most common forms of dementia.

Structural magnetic resonance imaging in the practical assessment of dementia: beyond exclusion

Neuroimaging is increasingly used to aid diagnosis in dementia. The traditional view that imaging is important solely as means of excluding treatable causes of dementia is maintained by many guidelines. These conditions however, account for a tiny proportion (<1%) of all causes of dementia. Over the past few years it has been recognised that a more accurate diagnosis and prognosis is important for patients and their families. The different pathological processes that produce cerebral dysfunction at a cellular level also produce macroscopic effects that can be detected in vivo with imaging. Clinically useful measures that distinguish between neurodegenerative disorders at an early stage are still awaited. The most likely future use of structural imaging will be the identification of patients at risk for Alzheimer's disease or with preclinical Alzheimer's disease. For magnetic resonance imaging (MRI) this will mean focusing on those areas that are affected earliest in the disease; ie, entorhinal cortex and hippocampus, using high resolution structural MRI or sophisticated brain mapping techniques. Imaging research is also likely to focus on measuring progression and detecting therapeutic effect. As such, MRI is already become an indispensable tool in clinical trials in dementia.

Differential muscarinic and NMDA contributions to visuo-spatial paired-associate learning in rhesus monkeys

RATIONALE

Early, accurate detection of degenerative neurological disorders such as Alzheimer's disease (AD) is essential for therapies designed to slow disease progression. Performance of a touch-screen mediated visuo-spatial paired-associates learning (vsPAL) task predicts neurocognitive decline in elderly populations presenting with mild cognitive impairment and distinguishes AD patients from elderly depressed individuals. Translation of this cognitive task to a non-human model may therefore provide an improved tool for study of the etiology and treatment of dementia.

OBJECTIVE

The goal of the current study was to contrast cholinergic and glutamatergic contributions to performance of this AD-sensitive task by challenging rhesus monkeys performing vsPAL with muscarinic antagonist and non-competitive NMDA antagonist drugs.

METHODS

Seven monkeys were trained to perform vsPAL and then serially challenged with acute doses of scopolamine (3, 10, 17 microg/kg, IM) and ketamine (0.3, 1.0, 1.78 mg/kg, IM).

RESULTS

Scopolamine produced a dosexdifficulty related impairment of both recognition memory and incremental acquisition aspects of task performance. In contrast, ketamine administration resulted in a dose-dependent impairment of recognition memory but not incremental acquisition.

CONCLUSIONS

Monkeys' performance of a task sensitive to AD in humans was impaired by two classic pharmacological models of cognitive impairment, therefore supporting the use of this nonhuman model to explore mechanisms of AD-associated cognitive decline. The differential pattern of impairment observed is consistent with a hypothesis that muscarinic mechanisms are required for linking external events with an existing internal representation, whereas NMDA mechanisms are required for the formation/strengthening of such an internal representation.

Structural neuroimaging of Alzheimer's disease and other dementias

This paper reviews the use of imaging techniques to aid in the clinical diagnosis of dementia. Two approaches are distinguished. One is the exclusionary approach in which imaging is used to rule out diseases that would mimic or cause dementia; based on the literature, this approach yields very little, if any, information that was not identified clinically. The more positive approach uses imaging as a diagnostic tool to identify changes specific for causes of dementia; any assessment of medial temporal lobe atrophy on Magnetic Resonance Imaging (MRI) will result in a reasonably high positive likelihood ratio distinguishing AD patients from non-demented individuals, but fails to distinguish AD patients from patients with other dementias. For a diagnosis of vascular dementia imaging is necessary, although not all vascular changes fulfill requirements of being relevant to dementia. Potentially of more importance, given the higher prevalence of AD, is the identification of concomitant vascular changes in AD that may be amenable to therapy, and may be used to identify subgroups. Structural and functional MRI techniques have great potential in identifying patients at risk for AD, which will allow for a very early treatment with drugs that slow or even halt progression.