[18F]FDG-PET study in dementia with Lewy bodies and Alzheimer's disease

Premotor and fronto-striatal mechanisms associated with presence hallucinations in dementia with Lewy bodies

INTRODUCTION

presence hallucinations (PH) are frequent in dementia with Lewy bodies (DLB), but their cortico-subcortical origin is unknown. Recent studies have defined key frontal and temporal areas contributing to the occurrence of PH (PH-network) and tested their relevance in subjects with Parkinson's disease (PD). With the present study, we aimed at disentangling the metabolic and dopaminergic correlates of pH as well as their relation to a recently defined PH brain network in DLB.

METHODS

for the present study, we included 34 DLB subjects (10 with PH (PH + ); 24 without PH (PH-)), who underwent ¹⁸F-FDG PET and ¹²³I-FP-CIT SPECT imaging. We performed ¹⁸F-FDG PET group comparisons, as well as interregional correlation analyses using ¹⁸F-FDG PH-network regions as a seed.

RESULTS

PH + versus PH- had reduced ¹⁸F-FDG uptake in precentral, superior frontal and parietal gyri, involving ventral premotor cortex (vPMC) of the PH-network that showed strongly reduced functional connectivity with bilateral cortical regions. ¹⁸F-FDG vPMC uptake was negatively correlated with caudate ¹²³I-FP-CIT uptake in PH+ (p = 0.028) and interregional correlation analysis seeding from the vPMC showed widespread fronto-parietal ¹⁸F-FDG decreases in PH + .

DISCUSSION

these findings uncover the pivotal role of vPMC (involved in a PH-network) and its cortico-striatal connections in association with PH in DLB, improving our understanding of psychosis in neurodegeneration.

Clinical utility of FDG-PET for the differential diagnosis among the main forms of dementia

AIM

To assess the clinical utility of FDG-PET as a diagnostic aid for differentiating Alzheimer's disease (AD; both typical and atypical forms), dementia with Lewy bodies (DLB), frontotemporal lobar degeneration (FTLD), vascular dementia (VaD) and non-degenerative pseudodementia.

METHODS

A comprehensive literature search was conducted using the PICO model to extract evidence from relevant studies. An expert panel then voted on six different diagnostic scenarios using the Delphi method.

RESULTS

The level of empirical study evidence for the use of FDG-PET was considered good for the discrimination of DLB and AD; fair for discriminating FTLD from AD; poor for atypical AD; and lacking for discriminating DLB from FTLD, AD from VaD, and for pseudodementia. Delphi voting led to consensus in all scenarios within two iterations. Panellists supported the use of FDG-PET for all PICOs-including those where study evidence was poor or lacking-based on its negative predictive value and on the assistance it provides when typical patterns of hypometabolism for a given diagnosis are observed.

CONCLUSION

Although there is an overall lack of evidence on which to base strong recommendations, it was generally concluded that FDG-PET has a diagnostic role in all scenarios. Prospective studies targeting diagnostically uncertain patients for assessing the added value of FDG-PET would be highly desirable.

Clinical Neurology and Epidemiology of the Major Neurodegenerative Diseases

Neurodegenerative diseases are a common cause of morbidity and cognitive impairment in older adults. Most clinicians who care for the elderly are not trained to diagnose these conditions, perhaps other than typical Alzheimer's disease (AD). Each of these disorders has varied epidemiology, clinical symptomatology, laboratory and neuroimaging features, neuropathology, and management. Thus, it is important that clinicians be able to differentiate and diagnose these conditions accurately. This review summarizes and highlights clinical aspects of several of the most commonly encountered neurodegenerative diseases, including AD, frontotemporal dementia (FTD) and its variants, progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), and Huntington's disease (HD). For each condition, we provide a brief overview of the epidemiology, defining clinical symptoms and diagnostic criteria, relevant imaging and laboratory features, genetics, pathology, treatments, and differential diagnosis.

The relationship between hallucinations and FDG-PET in dementia with Lewy bodies

Visual hallucinations are common in dementia with Lewy bodies (DLB), although their etiology is unclear. This study aimed to investigate the relationship between severity and frequency of hallucinations and regional brain glucose metabolism. We performed brain FDG-PET scanning on 28 subjects with DLB (mean age 76). The neuropsychiatric index (NPI) was used to assess frequency and severity of hallucinations. We used the SPM package to investigate voxelwise correlations between NPI hallucination score (severity x frequency) and FDG uptake relative to the cerebellum. There was a bilateral medial occipital region where reduced FDG was associated with increased hallucination severity and frequency. We conclude that the reduced occipital metabolism frequently seen in DLB is associated with frequency and severity of visual hallucinations. Further studies are required to investigate whether this is the result of deficits in top-down or bottom-up visual processing pathways.

Autopsy as Gold Standard in FDG-PET Studies in Dementia

Positron emission tomography (PET) imaging with F18-fluorodeoxyglucose (FDG) is increasingly used as an adjunct to clinical evaluation in the diagnosis of dementia. Considering that most FDG-PET studies in dementia use clinical diagnosis as gold standard and that clinical diagnosis is approximately 80% sensitive or accurate, we aim to review the evidence-based data on the diagnostic accuracy of brain FDG-PET in dementia when cerebral autopsy is used as gold standard. We searched the PubMed and Medline databases for dementia-related articles that correlate histopathological diagnosis at autopsy with FDG-PET imaging and found 47 articles among which there were only 5 studies of 20 patients or more. We were able to conclude that sensitivity and specificity of FDG-PET for Alzheimer's disease are good, but more studies using histopathological diagnosis at autopsy as gold standard are needed in order to evaluate what FDG-PET truly adds to premortem diagnostic accuracy in dementia.

(99m)Tc-hexamethyl propyleneamine oxime brain perfusion single photon emission computed tomography in characterization of dementia: an initial experience in Indian clinical practice

There is a growing health burden in developing countries due to recent trends of increasing incidence of neurodegenerative diseases. To reduce the healthcare cost and effective management of dementia illness, early diagnosis, accurate differentiation and their progression assessment is becoming crucially important. We are utilizing ^99mTc-d, l-hexamethyl propyleneamine oxime (HMPAO) brain perfusion single photon emission computed tomography (SPECT) to characterize dementia on the basis of perfusion patterns and observed significant improvement in their management. Eleven patients (median age of 60 years range of 53-83 years) with clinical suspicion of dementia underwent ^99mTc-HMPAO brain perfusion SPECT. SPECT-computed tomography acquisition done, data are reconstructed, reviewed in three view and further processed in “neurogam” to get voxel based analysis and the comparison with age based normal database and surface mapping. Final diagnosis was done with clinical correlation. Four patients are diagnosed as Alzheimer's disease, two as frontotemporal dementia, one as dementia of Lewy bodies, two as vascular dementia and two as pseudodementia. All imaging findings are well-correlated with clinical background. Brain perfusion SPECT with HMPAO was very helpful to us in characterizing the patients of dementia by its perfusion pattern.

Mapping changes in mouse brain metabolism with PET/CT

Because preclinical imaging offers challenges and opportunities, we set out to investigate and optimize image processing techniques to measure changes in mouse brain metabolism with preclinical (18)F-FDG PET/CT. In particular, we considered the effects of scan length, image registration methods, image quantification methods, and smoothing during statistical parametric mapping (SPM).

METHODS

A cohort of 12 wild-type mice was scanned on 3 occasions at an average age of 6, 10, and 14 mo. The impact of the scan length (10, 20, 30, or 40 min) was determined, and images were registered to a template based on either the PET or the CT image. Analysis was performed using SPM or predefined regions of interest (ROIs). Data were expressed in units of standardized uptake value or percentage injected dose per gram of tissue for absolute values; images were also normalized to whole-brain activity.

RESULTS

Significant variability was observed in global brain (18)F-FDG uptake between animals. Normalizing images to the whole-brain activity significantly improved detection of regional changes in metabolism. Registration based on CT images provided greater power for detecting changes in metabolism than did registration based on PET images only. In line with an age-dependent decline in brain metabolism, both ROI and SPM-based methods revealed significant changes; SPM, however, was generally more sensitive and region-specific. For example, small clusters of voxels within an ROI differed significantly between ages even in the absence of significant changes in average uptake over the whole region. Finally, and contrary to expectation, we found little benefit from longer scan times yet a marked reduction in uptake from 45 to 85 min after injection and regional variations in the rate of washout.

CONCLUSION

With appropriate processing, preclinical PET/CT provides a highly sensitive method for reliable identification of metabolic changes in the mouse brain.

Structure-Function-Based Quantitative Brain Image Analysis

Many neurodegenerative dementias produce significant alterations in the brain that are often not detectable by neurologic tests or with structural imaging. PET is ideally suited for monitoring cell/molecular events early in the course of a disease as well as during pharmacologic therapy. During the past 2 decades, molecular neuroimaging using PET and magnetic resonance (MR) has advanced elegantly and steadily gained importance in the clinical and research arenas. Software- and hardware-based multimodality brain imaging allowing the correlation between anatomic and molecular information has revolutionized clinical diagnosis and now offers unique capabilities for the clinical neuroimaging community and neuroscience researchers at large.

Imaging and biomarkers for Alzheimer's disease

The development of acetyl-cholinesterase inhibitors, and the prospect of future therapies to prevent, or modify, the course of Alzheimer's disease necessitates greater accuracy in diagnosis of this heterogeneous disease. Current diagnosis is based on clinical criteria and neuropathology. This is not always sufficient, and the development of sensitive and specific biomarkers would enable earlier and more accurate diagnosis. Genetic markers, such as Apolipoprotein E4, and cerebrospinal fluid markers such as beta-amyloid and tau, support a diagnosis of Alzheimer's disease. The latter can also predict conversion from mild cognitive impairment to dementia. Imaging markers improve diagnostic accuracy by reflecting brain function or aspects of in vivo pathological changes. In order for such biomarkers to become clinically useful, however, effective treatments need to become available, and long-term follow-up studies are necessary to evaluate the relevance of cross-sectional biomarker changes for the longitudinal natural history of the disease.

Fluorodeoxyglucose-positron emission tomography in the differential diagnosis of early-onset dementia: a prospective, community-based study

Background

The aim of this study was to evaluate the diagnostic accuracy of positron emission tomography (PET) using F¹⁸ fluorodeoxyglucose (FDG) in the differential diagnosis of early-onset Alzheimer's disease (AD) and other dementias in a community-dwelling population.

Methods

A prospective sample of 102 individuals presenting consecutively to a primary care centre for examination of suspected early-onset dementing diseases. The mean age of symptom onset of dementia in our patients was 60.06 ± 4.28 years (mean ± 1SD, 95% lower confidence intervals (CI) 54.75, upper 63.37). Patients were evaluated using standard clinical criteria for the diagnosis of dementia. Functional neuroimaging data was obtained and nuclear medicine physicians blind to the clinical diagnosis generated FDG-PET diagnoses. Final clinical diagnoses based on all available data were then established and compared against PET diagnoses.

Results

Forty-nine patients received a final clinical diagnosis of early-stage AD (MMSE score 20.97 ± 5.10). There were 29 non-AD demented patients, 11 depressed patients and a miscellaneous group of 13 patients. Among patients with AD, the sensitivity and specificity of FDG-PET was 78% (95% CI: 66–90%) and 81% (95% CI: 68–86%), respectively. The positive likelihood ratio (PLR) for a FDG-PET scan positive for the diagnosis of AD was 4.11 (95% CI: 2.29–7.32) and negative likelihood ratio (NLR) for a negative FDG-PET scan in the absence of AD was 0.27 (95% CI: 0.16–0.46). The pre-test probability was 48% and post-test probability was 79.02%. The specificity of FDG-PET in the differential diagnosis of other dementias, including frontotemporal dementia, was greater than 95%.

Recruitment methods in this study provide a sample that may be more representative of patients in the general population and indicate that FDG-PET imaging can contribute to the diagnosis of AD in younger adults with major increases in the positive likelihood rates and post-test probability.

Conclusion

The high specificity of FDG-PET suggests this technique might help in the diagnosis of frontotemporal dementia and other forms of early-onset dementia.

Metabolic correlates of brain reserve in dementia with Lewy bodies: an FDG PET study

BACKGROUND

Studies suggest that brain reserve allows patients with more years of schooling to cope better with brain damage. Research has been mainly focussed on Alzheimer's disease and no studies exist on patients with dementia with Lewy bodies (DLB). The aim of this study was to provide evidence for brain reserve in DLB.

METHODS

Twenty-one consecutive patients with DLB and 16 age-matched healthy controls were included. The participants underwent cerebral (18)F-FDG PET imaging at rest. A group comparison was conducted in SPM2 between the patient and control groups. A linear regression analysis with glucose metabolism as the dependent and years of schooling as the independent variable was performed. Age, gender and a total score of the Consortium to Establish a Registry for Alzheimer's Disease neuropsychological battery were included as covariates into the analysis.

RESULTS

The patients showed a significant metabolic reduction in the frontal and posterior association cortices, the basal ganglia and the pulvinar of the thalami. Glucose metabolism and education showed an inverse relationship in an extensive cluster in the left temporo-parieto-occipital cortex.

CONCLUSION

Similar findings were previously reported in Alzheimer's disease and are regarded as evidence for brain reserve. Therefore, we suggest that brain reserve is also present in DLB.

Diffusion tensor MRI to investigate dementias: a brief review

Diffusion tensor magnetic resonance imaging (DT-MRI) is a powerful quantitative technique with the ability to detect in vivo microscopic characteristics and abnormalities of brain tissue. It has been successfully applied to a number of neurological conditions, such as stroke, multiple sclerosis and brain tumors, providing information otherwise inaccessible on the pathological substrates. DT-MRI has also been used to study patients with cognitive decline, mainly those with Alzheimer's disease. Several image-analysis approaches have been employed, including region of interest, histogram, voxel-based analyses and DT-MRI-based tractography. Specific patterns of spatial distribution of tissue damage and correlations with neuropsychological measures have been reported. This review focuses on the use of DT-MRI to investigate dementias. The main clinical results and the different methods of image analysis will be overviewed and discussed.

Utility of the Bender Gestalt Test for differentiation of dementia with Lewy bodies from Alzheimer's disease in patients showing mild to moderate dementia

AIMS

We examined the utility of the Bender Gestalt Test (BGT) for the differentiation of dementia with Lewy bodies (DLB) from Alzheimer's disease (AD), comparing BGT scores between DLB and AD patients showing mild to moderate dementia.

METHODS

Eighteen DLB patients, 36 AD patients controlled by age, years of education, Clinical Dementia Rating and Mini Mental State Examination scores, and 21 nondemented elderly participants controlled by age and years of education were subjected to the BGT. Their BGT performances were scored according to the Pascal-Suttell method.

RESULTS

The DLB group showed significantly higher (that is worse) BGT scores than the other groups. When a cutoff point of 98 was used to differentiate DLB from AD, the patients exceeding 98 were 94% in the DLB group, 17% in the AD group and 0% in the control group. The sensitivity and specificity of this cutoff point were 0.94 and 0.89, respectively.

CONCLUSION

The BGT is a useful neuropsychological test to differentiate DLB from AD.

Differentiation of dementia with Lewy bodies from Alzheimer's disease using brain SPECT

We compared regional cerebral blood flow (CBF) patterns in patients with dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) using single photon emission computed tomography (SPECT) and investigated the diagnostic utility of SPECT study in differentiating between DLB and AD. SPECT data on 20 patients with DLB and 75 patients with AD were analyzed using three-dimensional stereotactic surface projections. Regional CBF reduction was determined by quantitative analysis using stereotactic extraction estimation method. The DLB group showed a significant CBF reduction in the temporoparietal, frontal lobe and posterior cingulate, similar to the CBF pattern in the AD group, but regional CBF in the medial and lateral occipital lobes decreased significantly in patients with DLB compared with patients with AD. Receiver operating characteristic analysis revealed that regional CBF measurement of the medial occipital lobe, including the cuneus and lingual gyrus, yielded a sensitivity of 85% and a specificity of 85% in discriminating DLB from AD. Objective and quantitative CBF measurement in the medial occipital lobe may be useful in the clinical differentiation of DLB and AD.

Brain tissue damage in dementia with Lewy bodies: an in vivo diffusion tensor MRI study

The aim of the present study was to apply diffusion tensor MRI (DT-MRI), a quantitative MRI measure which reflects tissue organization, to dementia with Lewy bodies (DLB). DT-MRI scans were obtained from 15 patients with probable DLB and 10 sex- and age-matched healthy controls. Abnormalities were found in the corpus callosum, pericallosal areas and the frontal, parietal, occipital and, less prominently, temporal white matter of patients compared with controls. Abnormalities were also found in the caudate nucleus and the putamen. The average grey matter volume was lower in patients than in controls. These findings of concomitant grey matter atrophy and white matter abnormalities (as detected by DT-MRI) in regions with a high prevalence of long connecting fibre tracts might suggest the presence of neurodegeneration involving associative cortices. The modest involvement of the temporal lobe fits with the relative preservation of global neuropsychological measures and memory tasks in the early stage of DLB. The selective involvement of parietal, frontal and occipital lobes might explain some of the clinical and neuropsychological features of DLB, providing a possible distinctive marker for this disease. The abnormalities found in the subcortical grey matter may indicate that DLB and Parkinson's disease share a similar nigrostriatal involvement caused by common pathophysiological mechanisms.

Dementia with Lewy bodies: a review

The dementia with Lewy bodies (DLB) is the second major type of senile, degenerative dementia, after the Alzheimer disease (AD). It is characterized by the presence of cytoplasmic inclusions of alpha-synuclein in the cerebral cortex and in the nuclei of the brain stem. DLB patients frequently have complex visual hallucinations, depressive symptoms, Parkinsonian manifestations and cognitive deficits, showing important associations with the Parkinson disease and the AD. The DLB should be differentiated from atypical Parkinsonisms, but the differential diagnosis often remains difficult and unsafe. Clinical and neuropathological findings, as well as neuroimaging are valuable tools in establishing specific diagnosis of DLB. Acetylcholinesterase inhibitors, dopamine-agonists, benzodiazepines of short or medium half-life, and antidepressants may be useful in the treatment of DLB, depending on the dominant symptoms of the given patients.

Neuroimaging as a diagnostic tool in dementia with Lewy bodies

Due to similar presenting symptoms, many physicians find it difficult to distinguish cases of dementia with Lewy bodies (DLB) from Alzheimer's disease or Parkinson's disease with dementia. The pathologic diagnosis of DLB has improved because of the discovery of probes for alpha-synuclein, a protein found in Lewy bodies. However, pathologic diagnosis can be employed postmortem only, and therefore diagnostic techniques that can be employed to guide patient management are still needed. Consensus criteria have been developed for establishing a clinical diagnosis of DLB, but they lack sensitivity. Therefore, a review of the recent literature was conducted to establish whether neuroimaging studies are useful diagnostic tools to help differentiate these syndromes. At least six types of tests can be used to image the brain of patients with dementia. Structural studies (x-ray, magnetic resonance imaging and computerized tomography) can disclose the presence of stroke sequelae and other lesions, whereas functional studies (magnetic resonance spectroscopy, positron emission tomography and single-photon emission computed tomography) can disclose metabolic and blood flow alterations that may be characteristic for different types of dementia. Although more formal studies are needed to confirm that these imaging techniques are reliable diagnostic tools for DLB and permit the establishment of guidelines for their use, neuroimaging techniques currently are being employed in practice to differentiate dementia types as a guide to treatment.

Imaging Alzheimer's disease: clinical applications

Extensive PET imaging research on AD has been conducted since PET scanners became available in the early 1980s. PET imaging using FDG, now commercially available, can detect early metabolic changes in AD and differential metabolic features of various dementing disorders. Image analysis techniques have also advanced in the field of functional brain imaging and permit accurate and consistent scan interpretation. PET studies that involve autopsy-confirmed cases suggest that the PET diagnosis of AD is no worse or may even be better than clinical diagnosis. Limited prospective studies demonstrated the effects of PET imaging in dementia management, which precludes the approval of FDG PET for more widespread, reimbursable use. Further evidence for the efficacy of PET imaging through well-organized clinical studies, as well as continuing efforts in technologic development and basic research to characterize functional alterations in dementing disorders in living patients, are equally important to achieve the goal of better dementia care.

Neuroimaging in dementia with Lewy bodies: metabolism, neurochemistry, and morphology

Dementia with Lewy bodies (DLB) is recognized as one of the most common forms of neurodegenerative dementia. Neuroimaging contributes to a better understanding of the pathophysiology of DLB by examining alterations in brain metabolism, neurochemisty, and morphology in living patients. Neuroimaging can provide objective and quantifiable antemortem markers for the presence of and the progression of DLB and permits differentiation from other dementias. This article reviews current neuroimaging findings in DLB with particular attention to occipital hypometabolism, dopaminergic and cholinergic deficits, and medial temporal lobe atrophy as measured by positron emission tomography, single-photon emission computed tomography, and magnetic resonance imaging.

Neuroimaging and early diagnosis of Alzheimer disease: a look to the future

Alzheimer disease (AD), a progressive neurodegenerative disorder, is the most common cause of dementia in the elderly. Current consensus statements have emphasized the need for early recognition and the fact that a diagnosis of AD can be made with high accuracy by using clinical, neuropsychologic, and imaging assessments. Magnetic resonance (MR) or computed tomographic (CT) imaging is recommended for the routine evaluation of AD. Coronal MR images can be useful to document or quantify atrophy of the hippocampus and entorhinal cortex, both of which occur early in the disease process. Both volumetric and subtraction MR techniques can be used to quantify and monitor dementia progression and rates of regional atrophy. MR measures are also increasingly being used to monitor treatment effects in clinical trials of cognitive enhancers and antidementia agents. Positron emission tomography (PET) and single photon emission CT offer value in the differential diagnosis of AD from other cortical and subcortical dementias and may also offer prognostic value. In addition, PET studies have demonstrated that subtle abnormalities may be apparent in the prodromal stages of AD and in subjects who carry susceptibility genes. PET ligands are in late-stage development for demonstration of amyloid plaques, and human studies have already begun. Functional MR-based memory challenge tests are in development as well.

Positron emission tomography and single-photon emission computed tomography brain imaging in the evaluation of dementia

The role of PET and SPECT brain imaging in the initial assessment and differential diagnosis of dementia is beginning to evolve rapidly. Numerous studies confirm the value of functional brain imaging, particularly with FDG-PET imaging, as a potentially cost-effective means of establishing an earlier diagnosis of Alzheimer's disease. Such an approach should allow for a more objective means of establishing which patients will benefit from treatment with cholinesterase inhibitors. In the future, neuroreceptor and plaque burden imaging studies should further enhance the sensitivity and specificity of dementia detection and patient management.

Functional brain imaging applications to differential diagnosis in the dementias

PURPOSE OF REVIEW

The diagnosis of dementia rests on an improved knowledge and a better detection of early impairments, to which functional imaging can certainly contribute.

RECENT FINDINGS

Progress has been observed at different levels. First, the understanding of different dementias has benefited from explorations of the neural substrate of dementia symptoms and from research into new markers. Second, diverse variables (clinical, anatomical, biochemical) have been related to impaired cerebral activity in Alzheimer's disease and other dementias, and progress in image analysis and in multimodal data acquisition has allowed a better understanding of the significance of brain activity disturbances. Third, functional imaging has been applied in well-designed clinical studies, and has provided important arguments for the diagnosis of characteristic clinical syndromes in the dementias.

SUMMARY

The functioning of neural networks responsible for clinical symptoms in dementia remains an important research topic for functional imaging. The development of new tracers and new techniques for image processing should also improve the usefulness of brain imaging as a diagnostic tool.